New leaks when switching to a synthetic oil from dino oil is a common problem - I've heard that its due to the synthetic oil having smaller molecules than the big long chains of hydrocarbon molecules in dino oil, but I don't know that for sure. That being said, I'm a firm believer in synthetic ATF, especially here in AZ with our high summer temps. I'm running an aftermarket transmission cooler in addition to the factory trans cooler, plus synthetic ATF, so that my transmission doesn't go up in smoke when I'm towing a trailer or rock crawling. I think the extra cost is well worth the extra protection.