Highly recommend taking it to the factory, they will get it right. Took our 2008 8315SS TT there this summer and had the entire floor replaced in less than a week. Very professional job and many other extras upgraded as well. They have the tools to do it right AND you want this issue fixed, for good. We are from So. Cal so we made a vacation of it and were fortunate to have family in MI to stay and visit while they had it.
In addition, since we were traveling in the TT, and not shipping it there, we had to empty it before we turned it over to FR, (in our case). A bit of a hassle but again, well worth it.
Sorry for your issue, best of luck.
GMC Sierra 2500HD Duramax
Rockwood Sig Ultra Lite 8315SS