The self-leveling air suspension is universally cited as the W112's defining vulnerability: cars sink over days to months when the front main valve or bellows leak, and correct repair demands rare valves and expert knowledge. Commenters point to bellows/struts being available and comparatively affordable, but leveling valves are 'unobtainium' and specialists (Star Motors / Neil Dubey, Martin Werminghausen at 600airsuspension.com) are the known fix.
Air suspension: the Achilles heel, servicing, and specialists
Mercedes-Benz 300SE (W112) Fintail · mechanical