1997 Lincoln Mark VIII front airbags

Suspension problem
1997 Lincoln Mark VIII V8 Two Wheel Drive Automatic 139k miles

similar to many owners of Mark 8s, mine is loosing lift up front overnight, but does inflate when started and holds during normal driving. I'm wondering what the most common cause is. Could it be o-ring seals at the pump? This seemed to be what happened in my 1984 Continental. How can I troubleshoot? Thanks for your help!