If you keep the air philer klean and run Yamaha R @ 32.1 with premium gazoline it shud last for a very long time.
I had a piston/ring assembly last for 8 YEARS on an '86 YZ490. Astonishing, what?
Yamahaha top ends last forever. And when your wears out, try to find a YZ360 kit that Noleen/Ohlins marketed back in the early 90's.
Remember, clean=long life on 2 strokes.