Getting ready to change the diff fluid and have a quesrion on which fluid would be best to use. The GM Synthetic Axle lube cost about $29/quart at local dealership which is extremely high compared to other brands. Mobil 1 for example is only $9.99/quart at all auto stores in the area. Is there any reason not to use the Mobil 1 over the GM brand???? They're both synthetic, same weight, etc. With the axle issues we have, I want to make sure I am using best fluid posible.