2007 GL450 Air Suspension

[USMCRO-5]

I have a GL450 with almost 190,000 miles and have owned the vehicle for 9 years. Through all the miles I've put on it, I've replaced both front air struts and both rear air springs. About a year ago, I replaced the air compressor. Now, when I come out in the morning, the front end is down on both the driver side and the passenger side. As soon as I open the door and the vehicle "comes to," (before I turn the vehicle on), the suspension will level off so I know that there must still be air in the tank. My suspicion is the valve block right above the compressor since it's about the only thing that hasn't been replaced. Thoughts?