How much was the front end going down in that few minutes?...an inch?....a half inch, or more? Don't know if your aware, but the car will automatically lower after you shut the car off and close the door, up to a few minutes. (a full inch on early models and a half inch on models after that) If it was going down more than that, you probably have leaking struts.
What happens most of the time is a leak goes unnoticed for 6 months or more before the driver even realizes a problem, because the system is all automatic. Because any air compressor produces moisture, when it has to run 2-10 times more due to a leak, that same compressor is going to produce 2-10 times more moisture. This is where the problems start. Being that the Mark VIII compressor is mounted on its side and the vent solenoid is the lowest point, if theres ANY moisture in the compressor area, gravity is going to bring it to the vent solenoid. The vent solenoid is basically a metal piston that goes up and down with a coil wrapped around it. If it has to deal with moisture for very long, it WILL rust and corrode. To learn a little more about this, go here:
http://www.americanairsuspension.com/MOISTURE.htm
A venting problem is quite common on a Mark VIII, but even more on a car that has had a leak. That brings me to the next question......Unless the vent solenoid in the compressor is stuck closed, which they are notorious for doing, the module "should have" vented all the air of the front struts. Since the car did not go down, I think you may have 2 problems(common also). One being a leak (frt. struts) and the other being a vent solenoid failure(compressor replacement).
The very first thing i would do is a leak test. This can be done easily without even getting your hands dirty:
http://www.americanairsuspension.com/MARK VIII LEAK TEST.htm
