Gerald,
Thanks for expanding on this fuel vent issue. Apparently my 2005 Monterey did not come with a check valve, just an open hose hanging down from the top of the tank. A couple of later model Monterey owners on RV.net confirmed the same arrangement. I think my solution will work for my coach. I don't know what model coach Dale Walker has, and since he implied only his passenger side fill port was slow I suspect your explanation is correct.
Now for the slide solenoid leak that doesn't leak. Sure enough Joel Ashley was right about the leak source. Turns out the leak is diesel fuel coming from this vent hose, which I had temporarily shoved on to the top of tank thinking it might have been siphoning. Well today I overfilled the fuel tank again (OMG) and discovered the excess fuel now runs off the tank top and travels down the coach framework directly to the slide hydraulic pump area. Now I am having a heck of time locating the hose, hindered by extremely tight space at the top of the tank; tried a coat hanger to no avail. Fired the Cat up, put on fast idle, charged the batteries and burned excess fuel. Until I get this vent issue resolved I'll be carrying a fuel tank and a siphoning hose cause I'm really tied of the mess.
Well believe it or not I have had some successes. I installed a 16" electric fan on the AC condenser, works great, psi was well over 300 and hot until until hydraulic fan kicked on. Added LED TV's front and rear with a sound bar system, replaced the old microwave/convection oven, mounted my old RF Mogul satellite and replaced it with the Eagle upgrade, replaced headlights with Mueller modification and replaced all marker and tail light lens. Many thanks to all this forums contributors and perhaps I'll get to meet some of you at a rally soon. 2016 will be our 44th year of continuous motorhome ownership, but this Beaver continues to be a fun and trying challenge for my fading brain.