oil filling primary cover

Another place that can allow oil from crankcase into primary is the screws that secure the rear half of the primary chaincase to the crankcase. I use some silicon sealant on them. 

Your breather arrangement seems odd to me too. The idea of the one way valve in the breather is to try and create a vacuum inside the engine, so that oil is not pushed out of the engine. You have another breather on the inlet, no idea why, that will effectively prevent the one way valve doing its job. I would try blanking off the inlet breather and see what happens. 

It could just be your engine is wet sumping  too much .  

Hi - I have a belt drive conversion so would normally run the primary side dry. However, I was getting some seepage into the chain case so I simply took the  cover off and rode around like that for a while so I could see where it was coming from. It turned out it was getting past the crankshaft oil seal so put a new one in. - not a difficult job if you are careful and you can request good quality seals from somewhere like Andover Norton. 

If you're running the clutch wet you'll still be able to cover a good few miles with the cover off without doing it any harm.

If you're leaving the bike for long periods and the sump is filling with oil, this is obviously not going to help matters. I've installed a quarter turn valve in the oil feed pipe between tank and engine. Guess I don't need to state the obvious..... don't forget to open the valve before running the bike!