I have owned an ATK 406 CC for 5 years. My old man bought it new in '91. It has been ridden all over the Rocky Mountain's eastern slopes and is still a wonderful machine. Rotax did not tune those engines for all out horse power, they have very strong torque from low to mid way through the rpms. The engines are very smooth and predictable but have a subtle European clatter (imagine ducati dry clutch sound) this does not mean the engine is due for overhaul, it is just the way it is. Just like any 2 stroke it will rev to the moon and will constantly remind you that your job is to hang on and steer. This bike is 24 years old and is still running the original piston and rings. You will be hard pressed to beat the Austrians at engine manufacturing.
Don't worry about the rarity of the machine, if it is in good shape and know how to maintain it, it will last forever (If you are looking for a good kids bike do not buy one of these).
The frame is nickel plated cromo and the only thing on the frame to have ever broken is a number plate mounting tab last year due to vibration.
Agreed the parts are hard to find but Keith at ADB is friendly and willing to go the extra mile to keep a customer satisfied, and when you talk to Keith you are talking to a guy who built ATKs new at the factory.
Honestly, I can not say there is a bike I would rather have for climbing mountains. If you are mature enough to enjoy a fine whiskey you will love this machine.
M.