Air suspension is weak
What do you mean, “weak”? Is the car sagging? Leaning? Higher in front or back? The compressor could be bad or maybe one of the air “springs.” You could have a leak in one of the lines. A good independent shop that does suspension work can probably get it back as good as new. If not, a Lincoln dealer should be able to fix it.
I believe there are kits to convert it to coil springs.
Hadn’t thought of that. An excellent idea.