.020 is quite alot to take off one of these heads. When warped they are usually straightened, not milled. Since it's done though, I would not worry about it.

My 124 leather seats are as good or better than any seats I've ever had in any car including my 96 E300 with orthopedic seats. There is most definitely something wrong, maybe broken springs underneath.

Yes the fluid motor mounts will make it shake like crazy when they fail. The passenger side is the one that fails due to its location near the exhaust manifold. I would change it first.

Enjoy and Merry Christmas,