Just happened to catch your problem. I have an M114 (250C) and before you start to tear into your motor I suggest you look at your cable. If it is anything like mine, the cable will have some plastic rings attached to it. These rings are what rides on the inside of the cable tube. Over time, they can break off and/or partially shear and that causes the cable to jam inside the tube. If that is your problem, a new cable (MB Dealer price) for my 114 was $80.00. Either your MB shop manual or a Haynes covers the cable removal. If it is similar to my 114 it is not a big deal.
Just passing thru - wanted to offer my experience. Good Luck.