Suspension Problems

[Cliffyoung]

I have a 1993 Lincoln Mark viii which has problems with its suspension. Everything with the suspension seems to work except it over-inflates the bags which makes the ride very stiff. I took it to the Ford Lincoln dealer in Baxter, MN. They didn't tell me what was wrong with it except that parts are no longer available and they recommended replacing the air suspension with a coil system. I don't think they knew how to work on it or how to diagnose the problem. I have the car at a shop that restores older cars. The technician there said that he put it up on a rack and felt the bags. He said they were extremely hard. It was on the rack for two days before the bags bled off their pressure. He then lowered the car and it rested on the floor in a lowered position. He then started the car and the air suspension started up and raised the car, however the bags again over-inflated. He said it seems that everything seems to work except it over-inflates the bags. I have had the car for 20+ years and I want to restore it and keep the air suspension. Can anybody give any advice as how to determine what is wrong with the suspension. Also, it appears parts are available. Is there any recommendation as to where to look. I apologize for being wordy but I am not very knowledgeable on this issue.
Thank you
Cliffyoung