I just wouldn't. Synthetic doesn't play well with rubber seals and o rings. I had the rear end rebuilt in my tool truck. We replaced the pinion seal 3 times because of leaks. (the shop used synthetic gear lube) We contacted a local company that specializes in bearings, seals, and hardware. They sold us a seal that took care of the problem. May be it's a silicone based seal instead of a rubber based. I'm not for sure.