Hey I wonder if anyone else has had this strange slow groan before cranking problem. I've had the same problem, and now some new symptoms. Car is a W210 M104 E320 (1996).
I have a new Optima battery and a new alternator about ten months ago. This was to not related to the starter issues, but to replace the worn out alternator (brushes) and not-too-old battery ( under warranty - Advance auto parts determined it was shot, who am I to argue
)
New symptoms started a week ago:
It strains when the key is first turned (10v), then begins to crank slower than usual (11v).
Idle: 13v
Idle in gear w/AC, all accessories: 11.98v
Engine off: 12.96v
Starting, as best as I can measure with my digital MM: 10v min, 11v while cranking normally
I think it's a starter motor issue, but I'm worried that there is a relay/solenoid/wiring/terminal issue I need to troubleshoot; the first step in that troubleshoot is Mercedesshop.com
TIA, -Tom