A piston and liner from the LA 25.
I had a GP 25 that would start and run happily in cold weather and never looked like starting when it was warm.
I replaced the piston and liner and the engine has been fine ever since.
It's been on a Ringmaster for quite a few years so, some years, it only gets one outing per year. I use auto transmission fluid as after run oil and it usually starts second or third flick after hanging on the wall for a year.