The SRC 6MM Complete Gearbox for MK36 is that the best thanks to upgrade your gearbox. Don’t make the error of thinking the sole way your gears can break is at the teeth. High power springs with mediocre bushings or bearings can break the gears at the stem. an opportunity at the stem is potentially more dangerous to the gearbox than simply a couple of teeth abruption . The SRC 6mm Complete Gearbox is meant to stop damage to the gears and to stop gearbox failure thanks to high stress. Stop worrying about which parts are compatible with what, or the way to shim. SRC has done all the diligence for you.