I doubt you need all these parts, but looking at it from the perspective of the mechanic, you have a problem that can be elusive to correctly diagnose and fix. The mechanic gave you a quote to cover all bases.
This is a case where the mechanic will keep changing parts until the problem goes away. As backyard mechanics, we've all been faced with this situations at one time or another.
If your engine wiring harness is original (you mentioned a crack - it's probably completely disintegrating!) it would be prudent to have it changed out. This is good money spent, and the problem may disappear with new wiring.
As for the OVP, the bad one is part number 000-540-52-45. The good replacement is part number 000-540-67-45. Again, this is good money well spent.
Depending on your relationship with the service department, you may want to have the mechnic requote with the above information. Have him address the wiring harness and OVP issue, then continue with diagnosis and repair if these two items haven't solved the problem.
95 E320 Cabriolet, 131K