So I posted a picture a week or two ago of my firebox after a bunch of tar had condensed onto it (still haven't figured out why ... wondering if maybe my door seal needs replacing). Anyway, much to my dismay, that hardened into a glaze-like creosote. I tried to break it down with this stuff: http://www.amazon.com/Rutland-98-Lbs-Creosote-Remover/dp/B00120NNCY but I just don't seem to be able to get it all. There's still a jet-black sheen over my entire firebox (although only 1mm thick, at most). I attached a couple of pics - you can see that while scraping I managed to get a few spots of bare metal to come through, so it's not thick at all. Here's my question, though: do I need to worry about this stuff, or can I just leave it be?