2008 Fleetwood Niagara. I got it a few months ago. I wanted to replace the AC gasket, but took the 4 bolts out inside, and it won't budge. Closer inspection seems to show that somebody sealed it on. I believe this was probably done when it was originally installed. I have the original manual for the RVP 8000 series AC unit, and it doesn't say anything about using sealant. Suggestions?