I just had a similar experience: By error I inserted the key for my W113 car. It went in smooth, but didn't turn. That's when I noticed I had used the wrong key. I couldn't pull it out. It was stuck. MB road service offered to come but cautioned me that they would most likely break the key off, using pliers. I made a tool: Looks like a slim jim: It's a blade made from .3mm thick sheet metal and 7.8mm wide. It was narrow enough to slip in besides the key on the left side. I made another one, same dimensions, for the right side. That one I cut a sliver out in the middle, longitudenally, about 1.2mm wide, to clear the ridge in the lock. When both are inserted, they lift the tumblers and I could pull my key out very easily.