Question for you guys who have put lots of miles on the NSR's.. How long do these engines typically last before needing new pistons? What about a bottom end rebuild?

..Just curious. My YZ engine specs every 30 HOURS. But that's a motocross race motor.. In an Aprilia RS frame..

..Anyway, just thought I'd ask and see how long these motors are holding up for.
I don't mind doing the rebuilding, but I don't know where I'd get a crankshaft..