At least it's not the gearbox casing itself. Mine completely snapped in two mounting points. It appeared that the prop shaft became loose and the resultant vibration (that only happened at certain speeds) caused the failure to the mounts and bent the prop shaft.
Gearbox casing is not a part available on its own. The gearbox was circa £8k plus vat alone as one fix, Add on labour and the propshaft and it was looking to be a humongous bill. Fortunately being that the auto box is found in a number of BMW's was able to get a salvage gearbox and used the casing from that.
