Thanks for the responses.

it was rebuilt by the PO, but he only did 200km after it was finished. Yes. it had new crank bearings and seals. Ok so im guessing its not going to be a simple fix. Will go for a top end pull down in the next weekend or 2. Thanks guys.

but from my reading that I have done around here, if the seal(s) have gone, wouldnt the bike fail to idle correctly? This bike idles like a peach. I only start getting problems over 4k rpm.