Starter problems or something else?
 

I have a 1975 450SL. Last spring it wouldn't start and the mechanic said the starter was bad, so we replaced the starter with a rebuilt one. Everything went fine until one day it didn't want to start and when I let up on the ignition switch (even pulled the key out) the starter kept cranking. I quickly removed the battery cable. Since the ignition switch had been feeling a little funny I thought that was my problem so I tore into the dash and when I removed the starter switch it fell into two pieces, so I ordered a new switch and installed it. Now when I go to start the car, the starter keeps cranking still. Any ideas, do I have a bad starter, a bad solenoid, or where do I start looking?
Thanks

You probably have a bad starter.

What you have is not enough spring tention in the solenoid to move the pinion which is under load off the flywheel ring gear. It is usually a matter of lubrication somewhere, probably on the solenoid piston which is not servicable on Bosch solenoids. It could just be a lack of lube on the pinion drive bushing and armature shaft. The pinion drive (starter drive) must slide back on the shaft for the solenoid to disengage electrically.

Thanks Steve, I will dig into it and see if I can squirt a little lube in there.