Can't fill my built-in propane tank

[LI-Camper]

Recently I have tried to get my built-in propane tank filled in preparation for camping. At two different propane filling stations, the propane would leak from the propane connector that screwed onto my tank. My tank fitting is clean and looks new as I keep the cap on it when not in use. At first I thought that the O-Ring on the propane station's connector at the end of the hose was faulty. However, the same thing happened when I brought the MH to another place to fill it up. Both filling stations just sell propane as a sideline and are not fully in the propane business.
Could there be a missing gasket on my tank fitting that causes the leak? The leak only happens when trying to fill the tank. I will bring the MH to a propane only business where they have propane mechanics if I can't solve this mystery. I have filled the propane several times before with no problems. Thanks for any help you can provide.

[mountainsam]

Great Post. something for everyone to look for. I learn something new every day.

[LI-Camper]

Old-Biscuit is correct!! My gasket is missing. I will get one pronto and a spare. I never had that happen before. Apparently the gaskets can come off when getting refilled so I will pay more attention next time. Thanks for all the help!!

[Bordercollie]

There is usually a propane odor after filling that goes away quickly even with good gaskets, etc.

[Old-Biscuit]

The ALL important fill valve 'gasket'.....check that you have one inside the fill valve

[midnightsadie]

I ,ve had this same problem theres nothing wrong,its the guy trying to fill with the wrong fitting. went to a propane dealer and he showed me the right one.

[pianotuna]

Take it to the local propane distributor--the one who fills rural tanks for the farm community.