I think that gap you're referring to on the window is normal, the window on mine has a gasket around it and why the window is slightly away from the metal. As for dirty glass, I need some serious cleaner regardless. The black crap that sticks on the glass is like black superglue. Windex, Oven cleaner, ash & newspaper, vinegar, Super Green, Orange Degreaser didn't even make a dent to it when I tried, and I started scraping it off with a razor. I later found out, the instruction manual says not to, as you can etch the glass and weaken it. Get yourself a bottle of Rutland Hearth & Grill Conditioning Glass Cleaner (broken link removed to http://www.northlineexpress.com/detail.asp?PRODUCT_ID=5RU-84&source=nextag&kw=5RU-84) I've tried many products and that one owns all others. I purchased an 8 oz bottle and I go through 1/2 a bottle a year. Definetely worth the $5 for it. One reason, it's a polish not a spray and it takes a little elbow grease using it, but all other products required a frustrating amount of elbow grease or only removed a light coating. Also, it makes future cleanings easier because it coats your glass with a special coating.
Definetely fix that gasket, and you may be burning wood that's too wet. The glass gets dirty when water in the wood comes out as steam, condenses on the glass, and while it's water on your glass it collects smoke particles which eventually burn and leave black crap that hangs on like superglue. Your air wash should be able to handle a little moisture in the wood, but it can't handle a lot. Also, now that you know the moisture in the wood is causing your dirty glass think of ways to prevent it from reaching the glass. Loading side/side helps, I would not do that front/back log you mention since the steam comes out the ends of the logs that front/back piece sprays steam into your air wash system. That can't be good. Also, the further back you keep your wood you'll find the cleaner the glass stays. But, if you have a gasket leak it'll interfere with the air wash system and your glass will dirty, usually in the location the leak is. Last, there's also a learning curve, when I first started my glass got dirty real quick. I didn't understand that moisture in the wood causes it, and that my wood was wetter than normal, and I was getting to know my new unit. After the first 3-4 months I learned how to load it, operate it, I worked harder on drying the wood and I'm now able to go at least 2 months without cleaning my glass it stays nearly spotless. I look back and can't believe where I started from, to where I am now. You'll find it more enjoyable as you get to know how your unit likes to be handled.
**EDIT Looks like I was beat to the punch