Im not 100% sure this applies to the MB starter as I have never taken one apart. However, often times the current is applied to the starter motor itself as a result of the solenoid coming forward. There are heavy contacts in the back of the solenoid that close then the solenoid goes out. It sounds to be line the solenoid is working ok, and the motor is working ok, but those contacts in the back of the solenoid are broken. You'll know for sure when you reinstall it I guess, but i bet thats whats busted. I have seen it happen many times on 6.2 diesels.