I use M1 in the tranny, crankcase, and diffs. For the coolant I just use the good ole green Prestone. When I was installing my 160* hypertech powerstat I noticed sludge coming out of the drain hole and the thermo housing. Not so good if you ask me, so I did the switch and has been running just as good as ever. BTW, the oil I am using is Mobil1 Extended Use Synthetic 5w-30 for 15k with a 7.5k filter change with Mobil1 filter.

Chris