For me it was my 1988 Yamaha DT200R, first one in NZ,i owned it for 15 years,did 80 odd thousand kilometers(fully regd,rode it to work ,club moto-x,trailrides etc)sold it in 2003 to buy our first house after i had just done a frame up rebuild,bought for $5.500 in 1988 and sold for$3.000 in 2003, it had two genuine piston kits in this time but was still on the original bore!(i pat myself on the back for running that in so well), bottom end had never been split but it was getting due because of the very few and far between odd neutral in the g/box, i have to admit i shed a tear when it left my house down the road on the back of a ute, man those bikes were tough! the only problem i had in the whole time was the powervalve crapping itself but it was fixed under warranty and never played up again.
cheers Dale.