The vacuum advance canister has no real direct path to the distributor internals in a stock Chrysler distributor. there are too many areas to vent any gas fumes out to atmosphere before it gets to the internals.
I doubt it's fumes.
It's possibly a worn distributor allow the shaft to move around knocking the cap loose or it's a bad cap.
They say there are no such thing as a stupid question. They say there is always the exception that proves the rule. Don't be the exception.
