I started using Mobil 1 5w-30 in my 98 OWB when I got it with 75,600 miles on the ticker. I've had no problems since, and have no oil leaks or any other leaks for that matter. I would check out Bob is the oil guy before doing anything. A lot of people use Redline synth in their transaxle and differential boxes, which isn't a good idea from what I've read and heard. IMO switching the engine and tranny fluids to synth is a good plan, but the other fluids I'd suggest sticking with dino.