I got a full garage of newer green stuff ('07 KX250 & older) & a mix of vintage yellow & green. One of the scooters is a '04 KX250 chassis/'02 KX500 engine conversion, which has been very reliable considering the condition of the bike that donated the engine (that we thoroughly rebuilt prior to plugging it into the KX250 platform). My '04 KX250/300BB & '03 KX250 have all been dead on reliable (once converted to race gas, no thanks to the ethanol pump gas locally eating crank seals for the few years it took for me to chase down the issue). I just did a complete resto on the KX300 after having around 8k miles & 3 years on the bottom-end since the last case split (top-end gets done at least once a year). It still ran fine, but with a 24HR race coming up and few other events I plan to hit this year, I didn't want to take any chances. I get a season out of linkage bearings or better. I'm still using all the original suspension components, powervalves, etc after 20k miles. I'm not the easiest on bikes (A rider) and the only bike that has managed to survive the kind of clutch abuse I (& my husband) dish out is the KX250's. I've gone through 3 clutch packs/springs & a whole inner/outer basket assembly in one season on the CR250 I used to race. I can get a whole season out of the KX clutch on the other hand and use the OEM basket for several seasons. Personally, I'm skeptical of aluminum frames (gun shy since the CR250 was like riding a tuning fork off-road, even with ridiculously plush suspension, too much trail feedback, aka rigid). I'm not saying KTM's or Euro bikes in general are poorly built (I worked in a off-road focused dealership for a decade where I sold KTM's, Kawasaki's & Suzuki's), just that most of my friends race on orange scooters (& some Betas, GasGas's, etc) and seem to have quirky issues and weird crap break on them.
Overall, the 2str Euro models seem good, but much like my dismay with a few design features on the KX250-R model (05-07 US) when they updated and shaved weight {like how minimal the cylinder skirt is compared to the older engine & being more prone to cracking the cylinder skirt in stock trim without a big-bore, the after-thought center powervalve spring off the governor rod that loves to break, etc.}, I'm concerned the additional weight savings is possibly going to cost longevity on the backside if your racing and keep them more then a season or two. Over half the miles of the 20k+ on my '04 are from off-road races, which is a pretty tall ruler to measure other bikes against durability wise (since most racebikes only see a few seasons, at best).
