With mileage like that, the only thing I'd worry about would be the primary chain. It has no tensioner. And a worn chain will start chewing on the engine cases. For everything else, continuous/regular operation is a good thing. If it runs well and doesn't leak, $900 could be a good buy. Of course, that is said without ever examining a specimen bike with 34 years of individually unique history.
It will have had several drive chains, sprocket replacements, tire replacements, head bearing replacement, swing arm bearings, wheel bearings, etc. Though, it IS possible that each of these routine repairs were done properly, by owners that truly cared for top notch, knowledgeable work, rather than minimum cash outlay.
Cheers,