Sphe,
Nearly any auto electric shop ( I don't know where you are located so I don't know if you have such things) can rebuild any starter; they have the sources for all the parts. Expect to pay anywhere from about $60 US to $120 US to have yours rebuilt.
I made a post recently about the solenoid; mine had been replaced as part of the rebuild however it was not a Bosch but rather an aftermarket. The problem was it didn't work IN THE CAR; on the bench it worked and tested fine. After checking it out, replacing, testing in the car, and then doing it all over again did we discover the problem. An OEM Bosch unit did the trick. Bottom line is ask for all Bosch OEM parts from your rebuilder.
Alternatively, you can simply "exchange" your starter at a Bosch dealer for a rebuilt one, and give them your old one in exchange. Just check with many foreign auto parts stores who deal in Bosch or check any of the MB suppliers in the links section.
Michael Salemi
1969 280SL
Signal Red w/Black Leather
Restored