The 6.9's self-leveling hydraulic (not air) suspension is praised as among the best-riding systems ever fitted, but owners flag it as the number-one maintenance concern at high mileage and hard to find someone who can work on it. US cars had a collar over the ride-height adjuster to preserve federal bumper height, and owners carry rubber support blocks in the trunk as a limp-home fix.
6.9 hydropneumatic suspension: best-riding but the weak link
Mercedes-Benz S-Class (W116) · mechanical