Working on a friends 04 GT
You have probably heard about the Dreaded Rear Mail Seal Failure.
First you will see something like this around the seam between the engine and trans.

You will start to have clutch slippage (not power loss ) ... the engine will rev, but you will accelerate very slowly if at all.
That means you have to do something like this

And when you take it apart you find stuff like this



At this point, it is probably a good idea to have the trans seals checked and replaced as well, if you have gone in this far, you may as well. Replace the main seal, o-ring, any hard parts as required (on this one they are fine) any bolts inside the bell housing (pressure plate bolts primarily).
Whoo hooo - and I said I was done with BMW clutch jobs after I did Pongo's Blue RT.