The owner's manual says to lubricate them from time to time with a drop of
engine oil or something similar.  I guess the previous owner forgot.  Give
the penetrating oil some time to work.

Earle

Hi TIA,

About 5 years ago, my 1997 Wrangler rear hinges really got stiff,
almost to the point of not wanting to move at all. It took a serious
effort to shut the gate, After years of trying all sorts of oils,
solvents, additives, etc., someone on this board suggested PB Blaster.

The key to PB Blaster is that you have to apply it several days in a
row and then again once or twice the next week. It sounds like a lot
of work, but its only a spray on each hinge for 3 or 4 days then work
the door back and forth for a minute or two. Then it may try to
stiffen back up the following week and you hit it again.

My rear door now swings like it's brand nes and that was a year and a
half ago that I sprayed it and haven't since.

Oh, truth in recommendation - PB Blaster does have a very strong
petroleum smell so you'll have to use it outside or with the garage
door open. The smell goes away fast, but I just wanted to mention it
so you weren't surprised like I was.

Good luck TIA