Mike,
This is important so take this advice very seriously.
Locate and learn where the Prevost body support points are for your coach. Gordon's link will help you with that, but if there is any doubt call Prevost. Supporting the coach while you are under it is very critical and it must be done properly.
Some of us use stands that were built for the specific purpose of supporting the coach. My daughter made them in her factory. Unfortunately it was a single run and there are none currently available. As an alternative consider using bottle jacks with an adjustable center screw of adequate tonnage. Make certain that they are tall enough so that with the jack in the fully collapsed position, but with the center screw turned up that it contacts the support points. That way you are not risking a failure of the hydraulic portion of the jack when you are under the coach. I also use air over hydraulic jacks that I got at Harbor Freight (http://www.harborfreight.com/cpi/cta...emnumber=97704) and they work well. The example I show via the link may not be the right jack, but it gives you the idea. They are also available at Northern Tool.
Once you do get under the coach and start looking around try to understand some basics. There is no air on the brake system when the bus is parked and you are not applying the service brake. If you want to check brake system connections for leaks you need to release the parking brake (chock the wheels) and have a helper apply the service brakes. That is the only way to apply pressures to the primary and secondary brake systems.
The aux air system associated with the suspension has air on it, but not on all fittings. When driving and in the driving position the air travels through the ride height valves via the 5 port Norgren valves, when the engine is off the 5 port Norgren valves lock the air in the air bags, and in the manual position, such as when leveling the 5 port Norgren is in the circuit to either deliver air to the air bags, or to discharge air from the air bags.
The suspension system on the bus is not one big system, but three separate independent supensions (front, left rear, and right rear) that happen to share an auxiliary air supply.
The points to seek leaks are varied. If the bus sits without leaning for long periods don't spend a lot of time looking at the suspension. Chances are good that it is OK. Keep in mind the aux air pressure can go to zero and the suspension could hold air quite well. The reverse is also true.
Places we have found leaks often are the pressure regulator in the rear above the door that controls engine belt tension. The belt tensioner bellows have leaked. The ISRI seat has had issues with the lumbar control switches. The floor slide cylinders leak from time to time.
For converter installed air circuits if you can plug the air supply to each until you find out which one you plug minimizes or stops the air leaks.
Look for leaks at air operated pocket doors if you have them.
Cold weather will make leaks show up quicker. Once you get the coach to a near leak free status such as the aux air compressor only runs once a day, it is easy to maintain that level of condition. Most owners let the little things accumulate then you are not chasing a single issue but many little ones.
Have fun, but be safe. Never ever go under the bus unless it is supported. I have a pit in my garage and even with the pit I will not get in the pit without having the bus supported.
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Gary & Lise Deinhard, 2003 Elegant Lady Liberty, Dbl slide
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