The main problem I find with Hylomar, is that it seems to loose it's solvent in the tube over time, making it unusable.
Wellseal, on the other hand, seems to last for ever. The only problem is the smell, but if you suffer from uncontrollable flatulence, you probably won't notice.

Brian, Sounds like you have cured the problem. Well done. Perhaps the pop you heard was a dead rat being expelled from your pipe? Now get out there and give it a damned good thrashing, just to settle things in.

Dear C15S,
Your locktab has been very badly made, possibly it arrived in the UK on a ship?
It should have a tab on it, and yours doesn't.
It fits as Mr. Brady says.
You can find what you are looking for on ebay, where you will clearly see a tab.

I've just had another thought. Is the screw hole adjacent to the leak in communication with the timing chest? If so, you may want to fit that screw with a sealant such as Hylotite Red, with, maybe a fibre washer.

Well, Brian, 150 lbf/sq.in. is good and would tend to indicate that you may not have too much pressure passing by the rings. It all depends on how concerned you are about excessive crankcase pressure. 'IF' your breather is blocked, then the pulsing will be more pronounced, but even if it is clear, I imagine there would be some normal pulsing as the piston descends.
My feeling is that assuming the mating surfaces are 100% and with new thickish gasket, the crankcase pressure would have to be considerable to force a leak, and I don't think it is. Are you certain it's coming from the joint? 
If so, I would try the Loctite product (leave it overnight before you start the engine). I wonder if you might fit the screws without the case, to ensure they're going in far enough to clamp the case? Someone might have fitted longer screws?
If you're convinced there's too much pressure, then try the Cylinder Leakage Test.
However, be warned that when you apply air pressure to the cylinder with the piston at TDC and both valves closed, as you further open the regulator, it will become increasingly difficult to hold the engine at TDC (Putting the bike in gear with the brake on certainly won't work.) If you get up to a high pressure and your jamming method lets go, it could be catastrophic.

3.3465" is 85mm, so it looks like your Sloper is 550cc.
I've just had another thought. It might be worth draining the crankcase, in case there is an excessive build up of oil. The drain screw for this is the upper of the 2 drain screws. If excessive oil is present, this will slow down the spinning of the engine and may oil up the plug.

Unless I have misunderstood your problem, you may be looking for a problem that doesn't exist.
Now that you have solved the quill problem, I would suggest you firstly carry out a Cylinder Leakage Test. You can find details on the Internet, although mostly USA.
Kits are available, but they are rather expensive, as you'll probably only use it once. I made up my own kit, but it ended up costing the same.
This will tell you if you have excessive crankcase pressure and more.
I had the same problem on a Vintage BSA, with sealant being pushed out of the joint by pressure (of which there will always be some). I tries all sorts of sealants, but having discovered the engine did not have excessive crankcase pressure, I used Loctite 518 and the problem was solved. I keep it in the freezer, disguised as a cucumber.
Do check the mating surfaces where it's leaking carefully with a straight edge. Perhaps you could loosely assemble the cover without gasket, and check the gap all the way round with a thin feeler gauge?

From the above, it would seem that someone has fitted an earlier barrel/head to 1933 crankcases, as the 1933 head was definitely separate.
Your head would have had a compression cup where your spark plug is. This is a brass cup, to which petrol was added in very cold weather, to thin the treacle thick oil on the bore, and ease kickstarter operation.
As you suggested, I believe that your engine top end would have had the spark plug screwed into the inlet valve cap.
Perhaps you might drill and tap you existing cap? However, I see no reason why it wouldn't start with the plug in a central position, but who knows?
The Part No. is R31, and you might try Cornucopia in Germany, or British Only Austria.
Not that this helps much, but it would seem that your Jug is from either a 1931 557cc or 493cc,or maybe a 1932 499cc or 557cc.I don't know which one of these would fit 1933 crankcases, as they were all different. Did you measure the piston?
It seems odd that it won't start as you seem to have everything needed. As I suggested, check the ignition timing on full advance. I would also physically check the valve timing against the diagram, and familiarise yourself with the pilot and pilot bypass orifices. Don't poke a wire down them. Check for blockage with an aerosol with extension tube. Your spark should jump at least 1/4" in air.
Splendid looking Motorcycle, by the way.

I always thought Jugs were something quite different?
I wonder what engine you have? A picture and engine number would be good.
The 1932 model had a separate cylinder head with no valve caps, just a spark plug hole in the centre.
The earlier models did not have a separate head, and had 2 valve caps and a compression tap in the centre.
Whatever, I think your engine should still start. Do you have good compression?
Is the spark plug getting wet? Are the valve timing marks on the pinions lined up? Do you have a spark? A neon tester would be a good start, but not conclusive.
Mag points should be just opening (use a cigarette paper) when the piston is about 7/16" BTDC on full advance?
Is there much play in the throttle slide when about 1/8" open? Is the choke slide bottoming?
Let us know, and we'll take it to the next step.

Perhaps you could warm it with a hot air gun to soften the adhesive?

Pay attention 007.

I suggested running a separate earth wire from the distributor to battery earth, in the unlikely event that the distributor is not earthing to the crankcase, for some nefarious reason. It shouldn't take too long.

Rhyatt is absolutely correct, but you don't seem keen to take his advice, offered more than once.
I think I might also run a separate earth cable from the distributor to battery earth, just to make sure. If you have a spark, I would also recommend confirming that it will jump 10mm as on the bench.
If it's still a weak spark, then disconnect the wire at the points, and just jab the wire to earth. This should give you your 10mm spark each time you jab. If you get a good spark, this will indicate that the points are the problem, perhaps assembled incorrectly?
Please make sure you disconnect all the loom wires from the battery, coil and points. If the loom is faulty (and it ran before you replaced the loom), leaving it connected could affect the results. Check the battery is still reading 6.4 Volts.
Regarding kickstart wear, bear in mind you have probably given it 10 years of wear over the last few weeks.
I'm surprised your knee is still working, but that is why you have 2 knees.

Is this a typo? I'm not sure that a spark at TDC fully advanced is quite right.
Dan, you need to make sure your magneto spark will jump a gap of around 8mm. No good holding the HT lead with your hand, it will move all over the place. Buy a Spark gap tester or make one, and let us know how big a gap it will jump.
When it won't start when hot, use your tester to confirm a good spark and then move on to carburation, or technique, i.e throttle open or closed, choke on or off, advance or retard etc. But do fit an insulator.

It's starting (no pun intended) to look like there is a problem with your wiring loom or connections.
So bypass the loom, and remove all the coil wires. Connect a new wire from the coil to the points, and connect a wire from the coil to the battery negative and start your engine. It shouldn't take too long.

Excellent. Now we're getting somewhere. So your new coil and battery are working well. You could test the old coil. It's probably OK.
I completely agree with Derek, although I hope you're bypassing the ignition switch and feeding directly from the battery? With this direct feed, I hope you're NOT switching the ignition on out of habit? Bear in mind that the bike started well before you rewired it. Don't forget to disconnect the feed before you pop indoors to bathe your swollen knee in Epsom Salts. I would also check the resistance between the points base plate and the 'distributor' body and the body to the crankcase. While you're at it, check the resistance between the battery positive and frame.
Are you sure the points are assembled correctly with 0.015" gap? Is there much sideways play in the 'distributor' camshaft bushes?
Are the advance/retard springs fitted and in good condition? I ask this because it could be that when you kick the engine over, the ignition goes to full advance, which may be why it kicks back?
Keep at it.