This one I have to go with the D4. Excellent stuff, even the redline MTL is ok.In my S I have used Redline D4 ATF, Castrol Dexron III, and currently Amsoil synthetic ATF. None of the fluids have caused any leaks. I have run with the Castrol the longest. I can not say any fluid is better than another because of the short time period each of the different fluids have been in the car. I will stick to synthetics because they have always worked well in the race car.