W124 starter problem
 

Hi, i have a problem with my 300D starter, when i turn the key it starts to crank very slowly like the battery is dead and gets real hot fast, it will pick up speed and start the car when the engine is cold but when the engine is hot it will not make one full rotation. What could be causing this, a bad connection or worn out starter brushes or something else ?

If the starter motor is getting hot, it likely has a shorted winding internally or the engine is binding up for some reason. If the engine runs normally and has no other mechanical issues, the starter is probably spent. You can check the main power cable going to the starter (disconnect the battery first!), but it sounds more like the starter motor itself is the problem.

It is worth checking battery and starter connections, and the ground strap from engine/trans to the body, just to make sure none of those are an issue, but most likely you need a new starter.