Thats my train of thought. Having grown up in Oregon myself, Im pretty confident that you only have 8 days out of the year where you have to worry about anything evaporating :)

The charcole canister was removed by the PO. I capped off the ventline because of the vision of raw gas fumes pouring into the engine compartment. I didnt think of air needing to go INTO the tube (duh).
Theres also a condensing tank on my wagon, mounted over the drivers side rear wheel, I left that intact, but I suppose that could get clogged up as well.

Im still waiting for a break in the weather to open up the throttle now that I uncapped the vent. That wagon never ceases to amaze me in the snow, but dont want to push my luck.

Let me know how it works with the older cap.
Im thinking Ill replace the locking cap on mine with a rag to give some ventilation to the tank. If car dies on the side if the freeway agin, then light the rag........