Air Suspension

Just got my hands on a 1996 Lincoln Town Car Signature Series with only 95,000 miles (one owner). Great condition except for the air suspension. When the car is running, the car is level; however, when it's parked, the rear drops down. Is this an air bag issue or do I need to have it checked out by a mechanic or dealership? Also, I've heard different stories about converting it to coil springs. Not sure what to do and whether to take it to a mechanic or dealership. Thank you.