I think you're right...the slots do seem to be normal. The REAL seal is the white, inner part.
I pulled the following codes today:
P0455 (1/6) Stored - EVAP System (Very) Large Leak Detected
P0456 (2/6) Stored - Evap System Very Small Leak Detected
P0455 (3/6) Pending - EVAP System (Very) Large Leak Detected
P0456 (4/6) Pending - Evap System Very Small Leak Detected
P0455 (5/6) Permanent - EVAP System (Very) Large Leak Detected
P0456 (6/6) Permanent - Evap System Very Small Leak Detected
I'm not one to just throw parts at a car, but a local dealer had a shutter and cap set in stock, for $34. Since the CEL went off for a brief time after a recent fill-up, I thought it logical that perhaps the nozzle being inserted and removed may have helped to temporarily seal a leak. It took some doing to get the outer cap off...four clips at about 2:00, 3:00, 10:00 and 11:00, and one at 12:00 that was very difficult to get to. I ended up cutting that bit with a hack saw blade. Anyway, when I got it off, the filler neck had five burls on it, like someone had hit it with a screwdriver and hammer. Not as deep as a chisel would go, though...still, maybe enough to cause a leak. I sanded them down with some 60 grit and 80 grit, and put an extremely thin coating of sensor safe silicon on the lip. I installed the new shutter set, cleared the codes, and drove it for two 15-minute drive cycles. So far, so good. My daughter is flying in from a trip at midnight tonight, and will drive it home. We are planning on taking it on an 8 hour drive to Gatlinburg TN on Thursday....fingers crossed.
The canisters can develop cracks that even smoke will not pass through. We use nitrogen to charge the system and spray soapy water, we use simple green with a 5 to 1 ratio. 5 water and 1 green. It'll find the smallest leaks.
I have never head that before, cuz I use nitrogen all the time, just never thought of using it in an evap system. But if you say it has an advantage, I would like to know what that is. Just curious, and I could easy rig up some kind of separate fitting to use with our smoke machine.
I also like the simple green trick, cuz I dilute my big blue which we use for AC leaks. The BIG BLUE stuff is expensive.
Nitrogen is a much smaller molecule and will find the smallest of leaks. We used simple green mixed 10 to 1 and sprayed things. Doesn't take but a few seconds to foam. Your smoke machine should have that capability.
I gotta ask... why would nitrogen work any better than air? Air is primarily nitrogen, with most the rest being oxygen, a molecule that is smaller than nitrogen. The only (common) gasses I see smaller are hydrogen and helium, but not enough smaller to be worth the bother.