At a certain point, nearly anything you buy will probably need to be serviced. Either a routine CLA or replacement of foam seals. If the foam seals have begun to corrode, those should be replaced first. Those tend to disintegrate into tiny very sticky globules, and you don't want that getting into the shutter where it most certainly will foul the mechanism or onto the focusing screen.

Make sure you check this when buying any SLR from the 1970s or 1980s. Cameras from the 1990s should still be OK.