I have this issue in a 300cd , well over 500k now . It can be that large pin that can get the wear , the slack if yours is like mine , just may require a professional service tech , you’ll have to get the rear of the car up and have it in neutral . I do all my own labor so theirs that to contend with for safety . Move the yoke of the differential and feel for slack in the engagement back and forth . It’s that pin that’s worn . Since you’ll need labor , new parts , the cost can climb . I’ve chosen to pull one out of a yard that’s good , just waiting to do this very messy job . It will feel like a different car once done .You can call around for the fix , maybe someone has one sitting around at their shop . Some older European shops hold on to good used parts just because Mercedes last like no other .