To seal off any unfiltered air?
It’s been a few months but I found what is turning out to be the answer. I added a bottle of Techron Fuel System Cleaner with fresh gas and it appears to have cleaned up any gum, varnish, whatever in the check valve…
The car starts right up each time now.
Added bonus, no “check engine” codes since.
Hopefully I haven’t jinxed it by reporting back but maybe this will help somebody else.
Cheers