Matchless G2 250 -Annoying Oil Leak

[DRC]

I have a small amount of oil leaking from the rear of the engine onto the front of the chain, this happens after it has been run, the bike i have only has the top chain cover and i have read something about a release valve that drips oil onto the chain from the rear of the primary cover, is this correct, just wondered if it could be fixed or if this is the way it should be to oil rear chain. Not having a lower chain case causes it to leak onto the floor, should this model have a lower chain case to catch the drips?

Cheers

DC