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.

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Current stable:
1995 E320 157K (Nancy)
1983 500SL 125K (SLoL)

Gone but not forgotten:
1986 300SDL (RIP)
1991 350SD
1991 560SEL
1990 560SEL
1986 500SEL Euro (Rusted to nothing at 47K!)

Gone and wanting to forget:
1985 524TD 167K (TotalDumpster™) [Definitely NOT a Benz]