First off, the 400ex is an air cooled machine.....that's old technology. Go with a Raptor 660 if you can find one - 2002 and later models. The 2001's DID have tranny issues, and it's impossible to know if you are getting one that's been updated or repaired. Just go with an 02 or newer model and you should be fine......the Rappy is the dominant trail machine, IMO. Can't beat that torque and fun factor - I prefer the YFZ450's myself, but that's because I'm an MX racer and I just like my quads low and wide and a little harsh feeling on the trails. There are a ton of good deals on Rappys out there....just make sure you pay attention when buying a used machine.....check the oil, check the appearance of the machine - look underneath it....just check to see if it's been taken care of. A machine that looks beat on the outside is most likely beat on the inside as well........be PICKY! Good luck!