I'm not sure how many hours on an Axial-Flow are too many, but with ~6400 engine hours I think our 2388 passed that point a few years ago. We keep rebuilding it, and it keeps running. Almost everything can be replaced, but with enough hours the things that are wearing out are getting more expensive and require more wrenching. There are points of failure that start showing up that aren't easily seen with a simple inspection, and sometimes replacing a few parts is just a band-aid over bigger problems. For example, we kept breaking sieve rails--fought it for several years, replacing bushings, making sure the sieves were timed right. We finally took out the entire cleaning system early last year, and found broken sheet metal around the auger bed and cleaning fan, as well as cracks in the chassis behind the flanges for the shaker drive bearings. The combine was quite literally shaking itself apart, and no amount of new bushings and shaker arms were going to stop it. Once we got everything welded up and properly stiffened, and replaced all the "consumables" that were worn, the sieves ran smooth as silk for the first time in ages.

If you don't mind doing the work, it's possible to keep a high-houred machine running. For only 150 hours per year, you could put a lot of work into a combine now and have it last a long time. I would not trust a "good to go," "field ready," or "just went through the shop" over the phone, though. Go look at it, bring some wrenches and a good flashlight, and tell the salesman to leave you alone for an hour.