Thanks for the responses guys. Yes, I have used the Hunter GSP (?) 7000 machine, and I can tell when it it works. I guess after dealing with this issue for a year or more now, I've been in "tune" with every little vibration that starts or stops - after all this is a Mercedes!
The tire store down here, using the latest Hunter gadget, tells me that the tires and wheels are ok. I have Continental Ecotouring, about 5000k on them. Would a bad tire cause the car to go out of alignment? I have had all 4 tires in all four spots on the car, several times. No help.
Also I forgot to mention in my original post - at about 38,000 miles I had new rotors and brakes put on. The car had to have another new set of ROTORS and brakes put on at 48000 miles. The pads yes, I could kind of understand, but new rotors after 10000k miles? Like I said, I drive like a weenie. Since the pull and vibration always coincides with each other, could the realignments conceal the problem for awhile? I've been to 2 different independent shops (very good) and then finally the dealership. The same results after 2 visits apiece with these folks.
I was considering getting Michelins soon, but wanted to explore all alternatives as well. Like I said, all 4 tires (and the spare) have been rotated into each spot many times trying to diagnose this problem. THanks everyone! I will pursue the stuck caliper next!