I'm not saying the 7075 cup isn't tough. What I'm saying is that if a rock gets wedged in there it will still gouge the outside of the cup. I'm sure it would still be useable but it would look like crap! I still haven't found anything that will clean silicone oil either. A poster in this thread mentions " essence f ", but I have no idea what he's talking about. I've tried every solvent I know of. Brake cleaner, carb cleaner, ether (starter fluid), gasoline, you name it. I asked local racers at my LHS what the magic solvent would be to clean the silicone oil out of my diff cups and they told me they knew of nothing that worked. They told me when the gears fail to just replace the cup. I even started a thread on RCTECH years ago asking this question and got basically the same response.