So I decided to smoke the system, but I could not find a leak. Found my smoker was blowing smoke and drops of mineral oil back toward the canaster so I used shop air and blew in all our from charcoal canaster side back to front. I used a pure baby mineral oil from Walmart … it was all they had... smelled baby fresh too.
Next, decided NOT to drop the tank as I was certain I could not do it in one day and disturbing so much on my car with almost 280K miles made me nervous. So I cheated and removed the back seat and swapped the check valve/ roll over valve. I put an air purge on the top side of the tank from underneath and used a Dremel to cut a lip open in the sheet metal above the check valve under the rear passenger side seat. I removed the check valve and gasket and they did not look damaged at all, no hairline damage or anything. I could not smell ANY gas until I removed it from the tank. I decided while I had the charcoal canaster cover off to replace all the hoses to the canaster too. I really don't know if anything I did helped the P0440 code or not. I used JB weld to seal the sheet metal back into position and will put the rear seat back in in the morning.
Guys, I don't know if I really needed to replace the check valve on the tank. Oh well, there is a new one there now...haha
I reset the code and will see if it comes back now. Let me know if you have any thoughts