EC250 Leaking oil through powervalve cover

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Hello!

My name is John and I am from Spain, I have recently discovered this forum so I decided to create an account!

I have an old EC250 from 2001 wich I enjoy ridding but I have some minor issues wich I would like to fix and learn in the process.

My gas gas leaks oil from left side powervalve cover, I have put a new gasket but still leaks oil, it is strange because leaks through inferior part of the gastket and through bolts hole, It is possible that cilinder's pressure is leaking through power valve?(see attached picture, that quantity of oil is after an afernoon riding with friends).

I have checked the vent tube and seems fine, but I cant see "where that hole goes" as i dont see any hole on the interior of the powervalve zone. Could the ventilation tube be clogged? Where is the entrance of that hole in the engine?

It is quite disgusting because sometimes I make little rides with normal clothes and my throusers and shoes get dirty with black oil. Moreover, I have plenty of friends with EC250 and EC300 and their bikes are always clean in that zone.

As far as I know my carburation is not perfect, usually when I check the spark plug is black, and to keep idling the idle screw is inserted all the way I think that low/mid range has much gas, high range feels great. I would like to improve the jetting but I have never taken apart a carburetor so I need to see some tutorials and learn first or find a good mechanic.

Thanks in advance!

EDIT: I add this link off google photos to see the attached picture with the best quality

https://photos.app.goo.gl/fiYqdTjDak6cd1de9