I guess what we are trying to say is this is a known problem area with the Comet set up regarding oil leaks. As you know, the adjustment slot cannot be sealed up to stop splashed up oil escaping via the main shaft, or it ceases to be an adjustment slot. There are some experienced Vincent fettlers like Greg Brillus or Ken Phelps for instance, out there who successfully manage to cure this by fashioning some sort of disc that fits perfectly around the shaft but isn’t fixed, allowing adjustments to still take place. These can be made from a flattened coke can amoungst other things. Ken did a write up on this once in MPH.
I think the other guys are referring to keeping the oil level spot on so making sure no oil is coming in from the engine and also making sure the primary chain case isn’t becoming pressurised? Mine is in with Mr Brillus as we speak getting sorted, which he has successfully done before but I’ve since had an Alton electric starter kit fitted by a non Vincent wise mechanic and it now chucks oil out constantly, or it did until I drained it completely in frustration and took to oiling my chain with chain lube through the filler hole. Not ideal I know, and I risked overheating my Conway (Honda) clutch.
I hope some of this helps.