Mine comes apart very easily, follow instructions in handbook. The glass slips into two slots at the top and then clips in at the bottom of the sides. No seals as such just a strip of rope like material that sits between the glass and the frame. All original. The only time I ever had soot like residue on it was because I'd put the coals back in wrong order, they have to go in certain places. It mists on start up when first used but it clears after a minute and is then fine for the winter.
The brass is, I think, lacquered. The only bit we have replaced are two brass strips that clip over the side edges of the glass, they went a bit pitted over the years. The trim on the canopy and the finials on the front stand are originals, never polished.