RE: OFFICIAL RC18MT/B/T THREAD
they sell shims but i think you only get 4 per pack. the reasons some diffs move is the gearbox will flex over time. as for plastic gears they will start to click even when shimmed right because they start to overheat then flex. also never re tighten diffs while hot. i did it with plastic ones and it destroyed it. lol
Associated RC18T Differential Shim Set (4) ASC21141