The dynamic bolster and massage function in the multi-contour seats is a near-universal failure point, blamed on an air-bladder system whose glued high-pressure lines let go over time. Sellers frequently report the seat heat, cooling and adjustment all work while the massage/pulse does not, and one seller joked that a working set is as rare as a three-dollar bill.
Massage/multi-contour seat air bladders fail
Mercedes-Benz SL (R230) · cosmetic