Planning on changing the transmission and differential gear oil, it's a 95 TT. The FSM calls for GL-5 80W-90 for the differential oil in my climate, Florida that is, but Redline only sells GL-5 75W 90, is that okay? For the trans, I'm using Redline GL-4 MT 90 75W 90. By the way, I'm new to this so go easy on me all you Z experts out there.