OEM chrysler out of the 03 T&C we just picked up was no better made than a stant. in fact, its failure was one of the legs on it snapped from the spring tension, warping the whole unit and allowing constant flow. rockauto sold me an ac delco for $5 and it went right in.
Someone above mentioned fluctuation--- I had that with a stant. Upgraded to a superstant and it was more constant.
I have done a couple of subaru t-stats... YES the oems always look beefier than aftermarket, BUT the 2 I've changed failed young at ~60k, and they failed CLOSED. I slapped a S-stant (i *think* it was an s-stant) in one of them (this is years ago, a 88 GL) and my buddy drove that car, leaking like a sieve, until maybe 6 years ago (he's in the navy). the stant lasted another 140k miles and 15 years.
That said, i think the plain stants are hit-and-miss off the shelf. Put one in a buddy's 1500 and returned it, and it's replacement, before going to NAPA (looked like a superstant) and got it right.
M