I needed a couple more quarts of ATF for my C4. I already have 8 quarts of Valvoline Type FA in it now. The local parts store ordered some up for me - but it came in as Type F. Doing a search on the Valvoline website didn't give me much. Are these ATF's interchangeable? My recollection is that they are virtually identical. Does anyone have an on line reference that I can look at for a warmer and fuzzier feeling?