Has anyone ever heard of using a synthetic motor oil instead of ATF in a standard transmission? I was told this by a local transrepair shop. I bought a 3rd gear synchro from them for my '95 F350 and inquired about the best fluid to use. The guy told me that Ford called for Merc 5 ATF but that he used a synthetic 5W30 motor oil. He also told me the reason for this was because it was used in big truck transmissions, and he had always had good results w/ it. Anyone ever tried this?