OVP failure symptoms (my 95 C280 + most others) include:
Stalling while at idle, when slowing down, and often when slowing down as you curve.
No hot-start. If engine is warm when shut off, and a re-start is attempted, the engine & starter will turn, but the engine might not catch; it cranks, but might not start.
An ABS (or SRS) indicator light, indicating low voltage.
Also, using the car to jump another car, or jumping your Mercedes often makes the OVP fail.
2006 E350 w/ 155k miles (Daily Driver)
1993 300E 3.2L Sedan w/ close to about 300k miles
2003 E500 Brilliant Silver (Had 217k miles when totalled!)
1989 300E with 289,000 miles (had for <1 yr while in HI)
03 CLK 500 cabrio (Mom's)
2006 C230k (Dad's)
1999 S420 (Mom's/Dad's)
2000 C230k Sport sedans
2001 CLK320 Cabrio (Mom's)
1995 C280 My First Mercedes-Benz... (155k miles. EXCEPTIONAL AUTOMOBILE. Was Very hard to let go of!)