And like my seals that I'm relacing, I called two reliable Prevost service people that I like (one older and one younger) to see what to refill the rear drive and tag with. The younger one said 85-140 EP and the other said 80-90 weight EP. I decided to put 80-90 in cause it just sounded right. They both said that Synthetic would not be neccessary since I only put 10,000 miles on a year. They both said every two years or close to that.