On one of my very good buddie's truck, he has knocked his rear pinion seal out 3 times, and it is now leaking again. The first time grass got into it and wraped, and after that they go about every 10 to 15 thousand miles. It is a 2001 2500 CTD quad cab long box that is stock. He runs 75/90 synthetic schauffers oil with the dodge additive. Any ideas of why it keeps knocking out the seal??? Thanx in advance!!!