DEFINITLY sounds like the OVP. A new one can be purchased here @ Partsshop for about $50 or so... pretty cheap. I replaced mine and I've had NO PROBLEMS starting the car since! I'd go ahead and replace it.
Also, you should go to the dealer and get a VEHICLE MASTER INQUIRY which will tell you all warranty repairs made by MBUSA, wiring harness might be on there. Have your mechanic take a look and see if it has been replaced. Good luck!
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!)