I had the optional air-ride, self leveling suspension on my 1989 Mercury Grand Marquis. At the time I was traveling in sales a great deal and the large trunk and air-ride suspension made for a great road car. With the Merc's relative, the Ford Crown Victoria, being every city's police car and every city's taxi cab, I hoped to drive the Merc for 400,000 miles.
The air pump went out at 110,000 miles, which was $1,000 to replace.
The rest of the air ride suspension began to leak at 210,000 miles and the estimates for repair were so high relative to the residual value of the car that I sold it to a mechanic, leaks revealed, for $1,000 at 220,000 miles.
Needed at new radio at one point, the rest of the vehicle was trouble free until I sold it.
I guess those police cars and taxi cabs do not have the air-ride option.
I was the only one that drove the Merc and it was almost all highway miles.
(Now I have a Ford Fushion. Almost the same interior room as the Grand Marquis, smaller trunk, V-6, gets 29.8 mpg overall, rather than 20.5 mpg of the Merc.)