This engine in my experience is maintenance intensive. If it hasn't been strictly maintained by the factory manual it becomes problematic as you describe. My '84 Eldorado with 4.1 now has 87,000 miles and runs beautifully, but it has been maintained by the factory manual using time interval rather than mileage based recommendations for servicing. If the car you are considering hasn't been strictly maintained according to the recommendations in the factory manual, I would be a bit leery of its potential for problems down the road.