John - I never did find a solution to solve my ride issues. Seem like you have similar issues. I always suspected the electronic shocks. The "good news" is, however, that as the miles accumulate in my XJL the ride is getting better. Now, with 24K miles the ride is actually "almost acceptable". Much of the time now it does not directly bother me, as opposed to when it was newer when I hated the ride.

I had given up trying to find a fix and the XJL is a leased car that is going to be returned in July. I will miss the luxury and the looks of the car but, certainly will not miss the ride experience. My XKR has a stiffer suspension but, ride much smoother.
None of that "pattering" vibration that the XJL always had.

Wish you good luck finding a solution.

Albert