Gas Cap

I am having trouble finding a gas cap for my monaco, i have tried all the usual suspects, autozone, kragen, pep boys, rock auto.

i now have 5 gas caps that do not fit! haha

i have tried purchasing the "wagon" version, and any other part number.

i even brought the filler neck into pep boys and test fitted every cap they had on the shelf

the tank seems to be original, but none of these fit, it seems like they need to go a bit "deeper" for the thing to lock into place, i do not want to drive the car because gas pours out when taking off from a stop.

any ideas? havent found many salvage yards that have old mopars around here, maybe some socal people can point me in a good direction?

thanks
Author: smallxfires