I''ve been using one since probably the late 80s. The only problems I have found are that the generator (the little tube that crosses over the burner to heat fuel) can get clogged or gummed up. That is easy to fix since they sell replacements for probably all models.

The second thing I would look for is to make sure the pump seal is in good condition. That is a small piece of leather on the end of the plunger used to pump up the pressure in the tank. Unless the unit has been really abused, a little 3-in-1 oil will usually fix it if it is not compressing the air properly. It is simple to check. Then plunger assembly unscrews, making it possible to pull the entire plunger assembly out.

My only other concern would be rust in the tank from improper storage.