Well, after working with them more, it appears that the cold has a minimal affect, if any. It seems that the engine RPMs are much more important. When decelerating, they work pretty much every time. When sitting still idling, they only work sometimes. So, we obviously need to have the engine in a condition of high vacuum.
Now that I know their ideal state of operation, I have just decided that there is really nothing wrong with them other than marginal vacuum. So....I am going to fixate on something on another car.
I guess if rear power headrests are my only concern on the S500, this must be one heckuva car!!!<BG>
Thanks for your ideas and help!!