I would look carefully at the lid and sealing area on the canner for dents, nicks, gouges, etc. Put the lid on & tighten it down to see if it seal properly. Look at the bottom to see if it is flat & not warped. No way to check to see if the guage works, (they are about $25.00). Check the lugs where the clamps go for cracks. Inspect the handles to make sure they are not loose. That's about all I can think of. A new one depending on size is over $200.00.
John