Check oil levels, level  plug below clutch worm drive. Excess oil will find a way out fast.

Walkers sell a drive side bearing retainer with a  modern seal in it, can be a touch tight on the threads if they are unworn. Original set up often works pretty well tho. Small oil seal can be fitted to genny drive too , requires machining a new bush, they may be a tech tip on this somewhere, if not there should be. . Will see if I can find one.

I am a little relaxed about oil leaks, I have to say. Most bikes of this age will generally weep from a variety of places, but with a little time and effort  you can certainly almost eliminate most of them. There is also a tendency for early leaks to slow and almost stop as felts become saturated and then clogged with oil and dirt. 

Weeps do of course prevent parts from corroding, but nothing should be bad enough to be spraying oil over your back wheel and brake. 

Any problem with the engine breather can magnify leaks too, particularly early days as the rings are bedding in.