Since refitting the gearbox seal cover plate into the back of the chaincase, with a new seal and new felt ring, it is very hard to spin the sleeve gear. I had expected the seal to slip over the mainshaft, but the sleeve gear comes through it. Is that normal? Also the felt ring is clearly being compressed to half its width or less - again, is that normal?
Everything you describe is as it should be, but I can't feel how tight your sleeve gear is to rotate. There should be some friction but try oiling the felt washer and also that you have the correct oil seal - the camshaft oil seal is the same size other than a smaller I/D, if you fit that by mistake in the sprocket cover the result is too much friction.
Thanks for the steer Rupert. I took the cover back off and checked the oil seal. I had ordered two seals: camshaft points and the clutch cover one. The camshaft points one is correct. But the other seal is an imperial one marked 1.187 - 0.750 - 0.250.
This translates to 31.75, 19.05, 6.35
My research shows that 30.3, 20.6, 6.3 is the normal sizing for 40-0243. I think that explains why it was tricky to fit into the plate, and too tight on the sleeve gear.
The old seal (retrieved from the bin) was marked 70-3833 which is the same as 40-0243. The larger id is obvious.