The OVP resides in a different location for the W124 series (wish it were THAT simple, though).
If the 2.8L underhood layout is similar to my 3.2L, then the OVP is actually located behind a black plastic shroud behind the battery. Push the top of the shroud down below the firewall lip and remove completely. The OVP is silver and has a clear top with a 10 or 20 amp fuse. It is bolted down on one side, so you will have to remove the nut before you can pull the relay off.
I disconnected and removed the battery for easier access. Total installation time: 15 minutes, including reinstalling the battery.
The part can be obtained for around $65 at FastLane. Not sure that the OVP is the cure (I had a different set of problems), but I hope it works for you.
2009 ML350 (84K) - Family vehicle
2001 CLK430 Cabriolet (71K) - Wife's car
2005 BMW 645CI (124K) - My daily driver
2012 Mustang V6 (60K) - Daughter's car