I am an idiot because it has plugged up before, though never this bad. I spent a couple hours today really cleaning the chimney out. Even the vertical above the horizontal was getting plugged up.
Before I cleaned the chimney out, I scraped the old door seal out, took the wire wheel to it, and installed a new door seal and silicone. It says it needs 24 hours to cure, so I'll light a fire tomorrow evening giving it about 36 hours total cure time. In conjunction with the chimney now freely flowing again, a properly sealing door should prevent creosote from dripping out of the door now.
I cleaned out the firebox as best I could. There is a lot of gooey creosote in the corners in there that needs burned off to get out. I vacuumed the ash tube after I cleared the ashes out of it. I vacuumed the tube the blower bolts onto.
I installed the new blower today, as well. Hopefully when I light this off again tomorrow night, all of the poor burning issues will be resolved and any leftover creosote will burn off easily. I'm going to burn a firebox full of cardboard first just to make sure.
Here's the new blower:
