It looks like a solid bike to me. A bit of oil smell shouldn't be a big deal, especially if it was sitting. It may be overfilled, I couldn't quite see in the CL picture, but I think it was to the top of the oil window. And the old oil will smell, it's degraded a bit, and will offgas.
I'd get it, and plan a weekend of maintenance. 2500 seems like a good deal. I'd change the oil and filter first with some cheapish non-synthetic (whatever brand name oil is on sale at autozone, etc) or Rotella T diesel, and put a couple hundred miles on it. Then do the spline lube, which is easily done with hardly any tools besides what comes on the bike, at most a basic mechanic's set. You'll need a sawhorse and some Guard Dog Moly grease. If it was a later model K75, I'd say you didn't need the input shaft lube, since it still (down)shifts well, but the earlier K's didn't have the hardened splines.