Okay, well ... learned a nice little lesson here. I knew something was up when I called mbpartswharehouse and got what was either an Indian or Bangladeshi call center - after making my way through two different CSR's I got a return authorization number.
The item is the exact same one listed on several online parts places and so i thought it was safe to buy. As it turns out, it wasn't. (with my BMW, you could simply call BavAuto and get what you needed - it appears the Benz parts world is different). I took the advice of a couple of kind forum members who suggested i contact Jonathan Hodgman, who isn't more than 2.5 hours away from me, and called him. He straightened me out and will be sending me the right OVP relay.
I am going to schedule a weekend to go over to ATL and have him look the car over and tell me what preventative measures I need to take to keep the car running strong.
Thanks again for all the help. I have a feeling this car is going to be much like owning a sailboat. Good thing I got a good deal on it, its going to cost me a fortune to keep ...