Why won't rear end raise up ?

My advice is to skip the replacement parts and just go ahead and convert to a coil suspension. You're just going to keep throwing money at the problem and it's just not going to get much better unless you're willing to fully replace the whole unit. Converting to a coil suspension will cost way less and end the repairs for good. Check out these guys You searched for lincoln navigator Strutmasters

I agree it's probably the air springs that are leaking. You have 2 good alternatives: #1 Replace those Lincoln Town Car Air Suspension Air Spring 98 02 with a good aftermarket replacement available at American Air Suspension. #2 Would be to do a Lincoln Town Car Air Suspension Conversion 9802 The ride is great and you'll never have those air suspension worries EVER again.

I have a 2000 Lincoln Town car, had the same problem, it was the rear air suspension/shocks. They are air bags basically that levels your car and it cost about $300.00 for each at the dealer for parts and install but it also has its own motor that inflates and deflates these air bags and I also had to replace that and that cost over $400.00 installed at the dealer.