Is it really necessary to remove the steering wheel on an SL? On the W124 and W201 of that vintage, the instrument cluster can be removed (pushed from the rear via the under dash panel) without removing the steering wheel.

The 10mm bolt is a tough one. It's best done with a helper holding the wheel while using a breaker bar and extension to free it. You will never forget the sound that the bolt makes when it initially loosen.