It sounds as if you have a bad Carrier Bearing.

The carrier bearing is inside the housing that bolts to the bottom of the car. This is sometimes called the Spider, but the correct name is the Carrier Bearing Housing.

If you can move the driveshaft around inside the carrier bearing housing then what has happend is this: You carrier bearing has frozen up and torn up your housing.

The good news is that the parts to fix this are cheap and the job is easy. The bad part is that it takes forever and you might have to pull the exhaust system to take out the drive shaft.

One thing to be aware of is that the driveshaft was balanced as a unit at Mercedes and will need to go back together the same way as it came apart, so mark the relationship of the front shaft to the rear one with paint before you take them apart.

Also try not to knock off any of the balance weights. If you do they are easy to replace by just sticking them back on with super-glue.

Do some research on how to replace the carrier bearing housing and bearing on your car as there is a bit of difference between the 115 and 123 versions.