I currently ride a 2001 RM250. I only ride in the woods, usually with the kids. I have ridden his 06 cr125 a pretty good bit and love how lightweight it feels, however feel the need for power at times. The other day I rode a yz250f and it seemed to be the best of both worlds. 4-stroke 250! How long do these engines last with proper maintenence, and non race conditions? How much to rebuild ?