The same thing happpened to my 97 E420. I had to change several parts to make it work properly

part #
210-821-15-51 Regulator $159
210-835-27-40 housing $36
210-820-09-17 Electric connector $ 29
210-820-68-41 Blower Motor $ 313


Total $537

If you go to a dealer they will charge retail $780 for parts + labor.. You are looking at over $1000 if they do it.

It took me an hour to do. I took off the underdash cover on passenger side. Removed the black blower motor housing. Remove the old motor and regulator combo. Installed the new regulator to the new motor and installed.

This is very common and it should be a recall item for sure

good luck