The caps are not universal, there may be a cap that fits multiple makes but not all. For your Caravan the Stant number is 10838. That number doesn't fit any GM models though.
It is possible to test the cap, however the time it takes for a shop to test it would likely exceed the cost of a replacement cap. To look at it visually you want to look at the rubber gasket marked with the arrow. It should be soft and pliable with no cracks or damage. Then look into the filler neck for any rust or dirt in the area the cap seals. Rust or dirt there will cause a leak. I have done a band aid repair on them if they are rusty, you use some fine scotch brite material to scrub the rust away then put a couple coats of paint over the rough area.
A common leaking point on the Caravans is the filler neck itself as they rust through and leak in the area between the tank and the fender. For that a smoke tester would be the fastest way to test for a leak.
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Monday, November 25th, 2019 AT 8:04 PM