I have several pre-war BSA's & a classic (1953) car. I use a FBHVC approved additive to do the following. It stops Ethanol attacking the non-ferrous metals (brass, copper etc) and also rubber components. It prevents valve seat recession (which only occurs over 3,000 rpm) and gives the fuel a 2 points increase in octane rating. I have been using this additive since lead was removed from fuel.( Millers VSp) I do NOT have shares or any other interest in this company!
3 of my re-war BSA's have very suspect valve guide lubrication and I use a spray grease on the valve stems by turning the engine over a few times before every run out. This works fine and I have done as much as 150 miles in a day without noticing any valve guide wear.
The problem of adding oil to the petrol, even at 80 to one, is that it will burn and accelerate the build up of carbon in cylinder head. Because it is burnt on combustion I doubt if any will lubricate the exhaust valve guide. Hope this helps somewhat