Recently, I found a leak in an 03 Audi Avant Quattro fuel tank that turned out to be a cracked nipple on a valve that resides atop the tank (there are 3 or 4). After a little research i learned that Audi had a recall for many of these just for this problem. In the recall it describes how to reinforce and seal the nipple on one or two of these valves, but not all of them. Of course, the one they didn't do was broken. So, I ordered the stuff, borrowed the gun from my friends at the Audi dealer and made the fix. I was worried. I don't usually try fixes like this. It was not fun getting this tank out, but a new one was 1330.00! I saw that the Audi 2 part adhesive was obviously 3M DP8005, and the gun also a 3m part. The fix was cool. You basically build a wall around the valve with the provided barrier and weatherstrip and fill it with this stuff. It hardened and stuck to the tank unbelievably. I realize you could find this on your own but after doing this I realized how handy this stuff could be.
So, I ordered some more to keep on hand and bought the gun and mixing nozzles on ebay for under 40 bucks. The adhesive is cheaper through Audi than buying from 3M distributors! Anyway, I had a Saab with an evap leak the other day. I found the leak coming from under the tank pressure sensor. It is mounted near the pump module on a little pedestal that is sealed into the tank body, apparently cracked from the guy who just replaced the fuel pump. Its easily accessible from under the rear seat. This spelled disaster however, as Saab parts are getting scarce and very expensive. We handcrafted a little wall around the sensor base just higher than the pedestal it sits in out of cardboard and round weatherstrip goo. Out came the 3m gun and dp8005 structural adhesive! Of course that pressure sensor is NEVER coming out again, but what a nice fix. This stuff works on these black poly tanks! Finding this recall turned out to be a great thing. Now, i also bought some high quality epoxies that work in this gun too. For you guys that do this evap stuff, i think your gonna like this! Here's the recall and 3M link. Could bail you out big time if you break one like this yourself or be a hero when you fix the unobtainable tank, for good.
Audi reference# 20L8/JY revised January 2009