Sounds like my problem. I had a bad rim when it got cold it was to porus (sp). I spent 2 winters trying the dunk thing at a dealership. I finally brought it to a different dealership I told them my problem and told me to let them try it there way first if it didn't work then they would order me a new rim (on warranty of course). They did the dunk thing cleaned the bead and checked it for nails etc... Well guess what it didn't work. I brought it back to them and let them see it overnight. I put the bad tire on the tailgate and told them it was flat. I let them fill it with air and let it sit overnight. The next morning they came in and it was flat. Needless to say about 6 days later I had a new rim and no more leaks.
Don't let them keep doing that damn dunk test. You know that there is nothing wrong with the tire. Make them get you a new rim. I think DC might of had a bad batch of rims. I've only heard of this on the Reny's though. Do a search and you wil see this has been brought up a few times. I think I'm on every post. Goodluck
1990 Jeep YJ, Olivine Green, SBC 350, 700r4 Tranny, NP231C Transfercase, Painless Wiring, Superlift 3.5" Lift 5/8" M.O.R.E. Shackles, 33" tires. Dana 44's front and rear 4:10 gears, And a Whole lot of Money