Allan--I found a shop in South Florida that specializes in these problems. They will diagnose and rebuild your units for substantially less. When I dropped off my car with them, they told me right away that the actuator wires fry due to heat (specially on the V12 motors, which generate lots of heat). The second culprit they thought was the wiring harness, which also deteriorates due to heat, and is very easy to check. In short, trial and error is probably the answer, but try to replace the expensive parts last!!!