Guys I having this feeling about NEED changing out my rear diff fluid again.( but i dont know I need to or not ) I replace pinion seal on my rear diff 300miles ago. change out oil with lucas 80w90 with ford LSD addictive. Reason I pick lucas cause the bottle say " running cool and quiet ", and all I heard about lucas is it heavy and thicker, since cold weather coming up, im affaird it will be too thick for cold weather. Guy tell me that " lucas is fine and you good for 30k miles , leave it alone " so I can get over this feeling it need to be change. If I change out, im going to run 80w90 valvoline with ford lsd addictive.