I had changed the oil in the Getrag before I started reading this site - the guy at the auto parts store said to use 5W-30 oil, but did not say anything about synthetic. So, is this thing going to be OK to drive for a couple of weeks until I can drain and refill it? It's already got over 200,000 miles on it. It seems to be working fine now, but I don't want to damage it by driving it with the wrong oil in there.