[Kajtek1]

"MB starters last forever". I had to replace starter on my SL500 at 192k miles as the freewheel gear broke (sounds like you have that too).
Removal was not that hard once I removed some shielding, but MB put high-torque on bolts so you really need good wrenches on it.
Recently I was also installing new starter on 624 engine that I was replacing and that one is hold by transmission bolts.
Can you post a picture what set up you have? Can't imagine MB made it too hard.

 

[Kajtek1]

Here is a site with generic info http://www.mercedesmedic.com/starter-replacement-the-easy-way/

 

[Kajtek1]

Looks like you have the setup where transmission bolts hold the starter.
Go under the car with socket, long extension having wobble on the end, or UV joint.

 

[Kajtek1]

You can gain more space there by dropping transmission mount, or lifting engine side.
But those things require good jacks and careful work as you can get your fingers catch in the way.
Be careful.