I bought a lightly used, Osburn 1600 insert from 2006 (give or take a year). I had my chimney sweep install a liner, a couple bricks, and a new gasket on the door. He put a 1/2" gasket in, and the door was absolutely not air tight. There were probably 1/8" gaps in the door, even when I adjusted the handle. So, I installed a 5/8" gasket from my local hearth store, and have been burning air-tight for weeks. I'm wondering if anyone else had this issue with "standard sizing" on their 1600 or Osburn. Most sites I checked mentioned a 1/2" replacement gasket size. I'm hoping someone else can find useful information from this post, as I had little to go on, other then some sites that mentioned a 1/2" replacement gasket, and one that mentioned a 5/8" gasket.