I think FLM make diff cases for the 3905 spec diffs ( they are different internally vs the 3906 diffs ), but I doubt it'll make a huge difference really; the money spent upgrading the stock diffs still wont make bullet proof as its the tiny spider gears that break- cant fix that without upgrading to 1/8 diffs. I'd just run the stock plastic diffs and tone down the throttle on the esc to spare them some stress.