I own a 2002 Monaco Windsor which is very close to yours, most of the parts are the same.
Do you have air leveling? If so yes, the "6-pack" can leak. Just do some searches and you'll find posts on this.
But the age of our coaches does require more upkeep. Last year while on a trip my coach started to loose air quickly after I shut it down. Prior to this the air pressure (based on the gauge) would stay up for days. All of a sudden it would leak down over night to where the low air alarm would come on when I started it, hadn't been doing that. Then it would leak down after an hour. Crawled underneath and sprayed down all the lines going to the tanks. Found all my pressure protection valves were leaking, some worse then others. I ended up cutting the trip short and headed home to fix. Wasn't a bad job but not easy to do on the road.
Also, there is another group, Monacoers.org Lots of smart Monaco people PLUS they have a greats parts reference book. Join that group and find the parts book and it will provide lots of info.
2002 Monaco Windsor 38 PKD Cummins ISC 350 8.3L
2005 Jeep Grand Cherokee w/5.7 Hemi