i made my own heady duty gearbox-mounts, will post some pictures if anyone is interested?
first off, i took the 2 original mounts, chopped off all the "flanges" and threads around the mount, so that i had just a square rubber thing with 2 metal plates on. then i drilled a 10mm hole through the mount.
took a third mount and did the same with this, and cut the mount in half. then i mounted the two orginal mounts on the car, took the third mount and sat it unterneath the beam holding the box, and put a long m10 screw with a locking nut through the whole lot

tightened it on hand-feel momentum.
bullet proof and fail-safe for almost nothing
sorry about my english, it's early in the morning...