Great website. I bought a Model 74 buck a month ago. Installed in a conventional fireplace with flex ducting all the way to the top. Last week I noticed the exhaust cap was discolored and upon further inspection saw a slightly liquid tar dripping off of it onto the chimney cap. I guess this is creosote, but can you only burn this stuff out? It doesn't clean off even with degreaser. I am burning cutoffs from a pallet company. Thanks for the advice