I have been running 30% on all my motors with no gumming up of oil issues,
I have had that problem with 25%, so see where you are coming from.

Even with the freshly Cleaned after the stripping it down, It is as if the sleeve has gained more pinch at the top or the piston has expanded slightly.

I guess the only thing is more heat to see if it will turn over.
Cheers again.

Appreciated.