I’ve only had my diesel heater for a year and I don’t use it very often. I also seem to have a faint smell in the heated air stream (not a diesel fuel smell). I checked the air with a handheld CO monitor and a combustible gas monitor as a safety precaution and both gave no indication of a problem. I scoured the internet and most say the smell will go away after extended use (mine hasn’t). I’m glad to hear that someone else has the same problem. When i disassemble mine for cleaning, I will check the seal you refer to. Thanks for posting.