MJ, this being an official BMW workshop they have failed in a very basic task OR have been very unlucky (it happens) BUT they are responsible. If they fail to look after you name and shame relentlessly on the net, youtube etc to teach the bastard a lesson in good business. If you are left to wear it, the repairs you mentioned are all doable if you did the work yourself, to have it done properly by someone will be very expensive, and you are not going to trust the shop you already dealt with. If i was in your position, mindful that you are in Singapore, i would be looking for a used g/box from a later 1100 (m97) likely from the U.S. or even australia. Wishing you the best in this drama.