I dont think I've bought a single item for my xt600 at a local dealer. Everything is from the internet, ebay end Kedo in Germany mostly. So I wouldn't worry about parts.

Be carefull not to ride at too low rpm's aswell. I had a buddy gear his bike 16/42, trying to get better mpg. He hammered half the nuts inside the engine loose. With stock gearing I would keep a minimum of 3000rpms in 5th, and preferable a couple hundred higher. If you gear it to get longer legs than stock, add a couple hundred rpms more.

If not abused, the bike will go on forever. I know people say this with every bike, but the Xt really makes it true. If you know the history of your bike, there should be no real surprises, other than the age-thing. The rubber-intakes, perhaps coils starting to act up ect.

As for maintenance, my bike has 6000km between oilchanges, i think yours is the same. And that is with whatever oil was a standard back in the 80's, a lot has happened in 30 years. I know oil is cheap and all, but no need to change the oil all the time. Sparkplugs last about forever, too. I usually go 15.000km on an oilfilter, because theres never any stuff in it. If I was anything about a 100% sure, I would change it more often. I even cut a filter open after the topend rebuild, nothing was in it. My bike has oil in the frame aswell, at around 80.000km I checked that too, it came out nothing but clean.

Valves are super easy once you know how to. Its under an hours work, if you take your time and enjoy a cup of coffee. Mine dont move much, I usually just have to adjust a few 1/100mm to set the right in the middle of spec. At 17.000 miles on a '86 model, adjust them now and forget about them for a looong time. If they're a bit tight on the intakevalves, it makes starting the bike harder.

Yours might be different, just wanted to give you my oppinion. Im just over 150.000km, with the topend rebuild at 125.000km for the first time.

We need to keep thesse bikes up and running, soon there will no bikes like it.