Thanks everyone for the replies!

While I did not use a thermometer, both front wheels feel warm but not really hot.

The pistons in the caliper move in and out as they should and after jacking the car, they do not seem to be dragging.

All sets of pads (three sets now) have had nice even wear on all four.
set 1 was on car when we got it and looked almost new. Previouse owner may have sold car over this issue.
Set 2 I bought online. I may have put 1500 miles on them before I purchased set 3 from Mercedes.

The second warping was on a trip to chicago and I drove the entire trip. I know that my foot was nowhere near the brake pedal.

Please keep the thoughts and ideas coming!