You can do it !!
It ain't no piece of cake but here's what I remember when I did that re-build on my 87 300E. I can't remember the exact order,
I sold the car and passed on the literature I had accumulated to the next owner. But here is what I remember. Before you dig into it confirm that it's not just the blower control switch inside the car. You can hook up 12V directly to blower motor at the connection under the hood on drivers side behind and near the brake booster on ;the firewall. If you go for removal do these steps. did you find my posts where I described what I did ?? Search post of: DanielW It's old but should still be there.
You have to remove the chrome strip at lower windshield, just snaps up with a wide putty knife or plastic trim wedge.
The entire wiper assembly has to come off entirely: notice how it is installed make sketches if you need to. The wiper arm has to be manually rotated I think I remember it is nearly straight up for removal ??.
The entire black plastic Blower housing around the heater air intake and all related rubber hood seals have to come off. Don' t force any of the pieces they may be old and brittle. There are some nearly hidden screws which all have come off. Seem on mine I had to use a really short phillips screwdriver for some of the screws.
There are clips on the top half of the blower motor --- release these and a single strap clip around the motor will release and allow motor and blower cages(2) to come off as a unit.
I lubed the shaft bearings with moly assembly lube thinned with laquer thinner (which of course evaporated leaving the lube behind) For the brushes (which were worn out on mine) I sanded down some GM alternator brushes which were a little too large and soldered on the wires at the needed angle to work like the OEM brushes. Used JB Weld to hold copper wire at correct angle. Sand contact area on the armature to the exact circle shape so it would touch same as old ones.
Good luck on yours...... or pay the indie or MB man a lot of labour charges . Unless you like tinkering and have done this sort of stuff before you may be safer hiring it done.