Picked up a 2000 YZ426F with the piston seized. Rebuilt the top end, but not sure what caused it. Before I start it up, I'm wondering if I need to put in the effort to check the oil pump? Looks like a bit of work to get to it. Can anyone tell me how often an oil pump can be worn to the point of failure or low pressure? The head had plenty of oil puddles in it when I tore it down. Piston had a half inch wide melted section at the rear of the piston, and the rings were stuck in the compressed position. also found the cam chain very stretched, and it kinked, and stuck between the case and crank gear. It was locked up as a result. Wondering if that could have somehow caused the whole event? Can't see how, but what are the odds of both happening at the same time?