Originally Posted by DaveW

If the car rolls too much through a corner and picks up the inside rear tire, it will unload and spin, trashing even the best diff. It is true the steel diffs can last longer... i found out that the plastic diffs will last long enough to get too much slop in the outdrive slots and need to be replaced before the diff gets gritty. Check the underside of your car after every run to see if it has rubber buildup on the corners of the chassis, this means it is rolling through the corners too much and is most likely the reason for your rear diffs demise.