First off I would just like to say that I really like this stove, and it has been keeping my house very warm. The problem I am having though is that after the stove has been running for an hour or so, I'll start to see the upper right hand corner of the glass window start turning black. I have tried three different brands of pellets, but still have the same problem. I also give the stove the stove a good cleaning each day with my shop vac, including behind the baffle plate, scraping the burn pot and basically keeping everything clean. I also have the OAK installed as well. I usually allways have the blower running a couple points ahead as well, like 3-7, or 3-3. Could this be the result of a leaking gasket around the glass or door? I have posted a couple of pics below.