YS640 Chimney Seal

I've had my YS640 since mid January. It is, by far, the best smoker I have ever owned. While there's will always be something new to learn, I have produced some pretty good results. I have experienced one small occasional problem, and would like to get other thoughts. Each time uncover the smoker, I pivot up the smokestack to vertical, push it in tight (?), and lock down the set screw. In spite of that, I seem to get some smoke leakage out of the connection, which I don't really consider a problem. What's more annoying is some sooty condensation that forms and drips out of the bottom of the chimney connection, dripping onto the concrete and leaving a relatively permanent mark. This might be more of an issue at the start of the smoke, when the YS640 is loaded and inside moisture it at its highest. It last occurred 2 weekends ago when I smoked 6 pork butts at around 60 lbs. I believe I pre-heated appropriately before adding the meat.
Could I wrap a piece of Big Green Egg style Nomex gasket around the leading edge of the chimney to create an air tight seal? Would that invalidate the warranty in any way?
Your opinions and/or comments would be appreciated.
Could I wrap a piece of Big Green Egg style Nomex gasket around the leading edge of the chimney to create an air tight seal? Would that invalidate the warranty in any way?
Your opinions and/or comments would be appreciated.