I've owned 5 of them since '85 and my last one was sold with 83K or so on the clock. I still see it around town occasionally. My current KLR has 45K, has never missed a beat and has needed absolutely nothing in terms of replacement parts..
That said, a poorly cared for KLR can be a liability. If you haven't already heard of it, the "doohickey" could be viewed as a design flaw in every KLR made from day 1 til today.. If it has a lot of miles on it or if the P.O. failed to stay on top of the cam chain adjustments the chain and cam sprockets degrade rapidly, wearing the teeth off the cams. For the most part the differences between a '93 and an '07 motor (last year of the "old" style KLR) were minor, consisting primarily of differences in clutch cages, etc.
If the P.O. "did the doo" early in the bike's lifem or was diligent about checking the stock "doo" and was conscientious about valve adjustments and oil changes in my experience they can be a solid 100,000 mile bike. If it has low miles and you're willing to assume said care and feeding you'll potentially acheive the same. Neglected, not so much.
Other than that almost any well-maintained KLR will still be standing long after the cucarachas have taken over.
The valves are bucket and shim which is sort of a PITA, but given decent attention to oil changes they seldom need shims. Mine has needed exactly 2 in 45,000 miles, but don't become jaded and fail to check them. I check mine at least twice a year, regardless of mileage.