Not sure if this will help but I had an issue with the cab bags leaking down. I never found a leak to fix but I put a check valve in the line before the bags. Never had in issue since and all it takes is to cut the line and insert the valve. Compression fittings so no tools needed only cost a couple bucks so very cheap fix.
Hi Been lurking and member for awhile but never posted. Have had a 05 Freightliner M2 as tow vehicle for a few years and recently bought a 14 Volvo 730. Going to try to work it for a bit then convert it to only RV hauler. Always looking for info about the rigs as I find them interesting. Involved in trucking industry for some time although never as commercial driver although licensed as such for years. Did lots of mods to the M2 so now its time to do it to the volvo,