All Racing brand out of China makes front and rear aluminum gearboxes. They hold the diffs. They look very nice and are on e bay. They are around $200. Good to know about the diff cases though, I see Tekno makes steel ones now that hold more fluid, they might hold up better than the aluminum ones when a rock gets wedged in there as steel is harder than aluminum. The plastic ones do look rather small though. This build is getting expensive with all the upgrades.