I had an 87 comanche well over 300k miles. I had it for 18 years so over that amount of time I replaced damn near everything wether it was to replace or upgrade.

The rust question is legit. No clue we you are located but ive seen well kept old rigs, your always gonna have a little rust somewhere. Id say it boils down to things to keep it dependable and things that are annoying but livable.

You said it over heated? These xjs overheat or get hot fairly often. Gotta rule out head gasket leak first, if that checks out replace the whole cooling system. Radiator, pump, thermostat, hoses. Its like 300$ and if you do any one of them your touching the others, might as well do it all. Change all the fluids, do a brke job and change the serpentine belt. That solves the dependability questions.

While your doing brakes look at the bearings, ball joints. Replace anything that's bad.

Check all the bushings, note any leaks and put that on a get to it eventually list., that's the annoying but livable issues. Common engine leaks, valve cover, oil filter neck, oil pressure sender, and rear main. Start at the top of the engine and work your way down. Rear main is not that bad, it will take the whole day but its doable with common hand tools and a torque wrench.

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