Hi Fille
Sorry to hear that you have caught the TC klackiti clack flu too.
The TC unit is fixable and as I referred to in an earlier post a few days back in this thread, you can open it up. Even if you open the tiny flap door and check if the cable gear moves with a bit of pressure, you can't see the broken teeth and must unplug remove the whole unit. (two small bolts)
See this post from another forum
http://forums.mg-rover.org/showthread.php?t=172482 
I used this approach to get at the cogs. Broken gear teeth seems to be the main issue. He actually molded new teeth with some tough stuff and shaped them. I luckily
had 2 faulty units and was able to salvage two good gears
and construct one fully working unit. The smaller gear is spring loaded so remove with care and take note how it is set up before you let the spring pop out. Fiddly bit.
Good luck