The best way to determine if it's an issue is to see what happens when you shut all the vents. If the temp goes down quickly and the fire goes out, the WSM is tight enough. I don't think my WSM is all that tight and my fire is out in about an hour. Of course, you can never say that charcoal is totally out in that short period of time because oxygen can reignite the coals for many hours or even days after the fire appears to go out - so be careful. Another way you can tell if the unit is tight is how much vent opening is needed to hit a certain temp. Again, I don't think mine is very tight because I can run about 250° with only one vent open less than half way. When my door was leaking badly, I could cook with all my vents closed (except for the top) and even with the top vent closed, the fire took a very long time to go out. Basically, if you can control the temp and the fire goes out, no need to worry about a little smoke leaking. It will always leak some.