When I got my 2013 SL550 home I had to go to the local dealer to get a few parts. My wheel did the same thing as yours. I went to the service department to see how much to repair it. The guy came out to my car, got in, moved the wheel way back, used his left leg to put upward pressure on it and slapped the rim hard with his right hand - It has worked fine ever since. He says users climb out of the car using the rim for assist and lock it up. What really surprised me - NO CHARGE! They have a new customer when I need them because of the way I was treated.
I also have a 2013 MB 550SL with the steering wheel jammed in the up position. I spoke to a rep at Mercedes who told me that the motor had to be placed at a cost of approx. $800. I read what you had done...tried it and it it WORKED. The only difference was instead of using my hand I wrapped a towel around it and hit it with a hammer. Thanks for saving me $800.