I agree with Caddyman on this point.
Retrofitting the car with conventional steel springs is definitely the way to go, for a couple of reasons:
As the mechanic stated, the complexity of the air suspension system is such that it is very hard to keep these systems functioning properly.
The cost of conventional steel coil springs will be much lower than the cost of replacing the many air suspension components that would be needed.
The book value of this 13 year old car does not warrant “investing” a huge amount of money for something that will likely malfunction again within a couple of years.