The mlst2 diffs have metal ring and pinion gears. if you boil the rest of the plastic diff parts you get a pretty solid diff. And with a mip centre ball diff and the losi dual disk slipper you have a pretty solid drivetrain.
The xray needs upgrades too before it's solid. You have to upgrade the xray to aluminium shafts and aluminium shocks (my plastic one leaked out of the box).