[The Prospector]

First thing I would do is pull the rear rocker cover off to see if there's anything obvious.

 

[The Prospector]

I've heard if you overdo the clutch push-pin mod it can starve the rear cylinder top end of oil.

 

[The Prospector]

The clutch pin modification involves grinding 3 flats down the length of the push pin (in the centre of the clutch) to allow more oil into the clutch but I believe it can take pressure off the feed to the top end of the engine.
The modification in well documented on here if you do a search and it might be worth stripping the clutch to see if a previous owner has done the modification.

 

[The Prospector]

My only comment would be, remember not oils are equal, I run a fully synthetic race oil, others will have different views, go with what you believe is best but don't go cheap.

 

[The Prospector]

I use nothing but full synthetic , moto specific oil. Be sure the race oil you choose doesn't need replacing more than usual , some are meant to be changed more frequently than normal and don't have the detergents in them.

Silkolene Pro 4 10w40

 

[The Prospector]

Each to their own, I use it in the engine, final drive and forks without issues.

 

[The Prospector]

I'm sure their gear and fork oil is fine , the name means nothing.

My original post was only to recommend the use of a quality oil not a specific brand. Most oil reviews concur that the more expensive oils use a higher grade base and better additives, so basically you get what you pay for.
As to knocking a particular brand or type I will keep my opinions to myself and reiterate my original post.. run whatever oil you wish just don't run cheap.

 

[The Prospector]

That silicone squeezing out of the rocker gaskets is way too much, if it's like that on the inside then clean it off or you're going to have more problems.