My screen sags in the back also, heat sags faster now than before and I have noticed cat fly ash worse with the screen sagging, not alot but worse than with the screen fitting tight. (same wood all along)My cat accumulates ash fairly rapidly. I've wondered if it is my wood (Red Maple, CSS about 20 months with first year outdoors), or if it is a strong draft (tall chimney with insulated liner, house out in the open). Just cleaned the cat during a "warm" day recently, and wife noted that it had only been 2.5 weeks since the last cleaning. It wasn't as bad as I've let it get before, but you could see a clear difference in the flames as the bypass was closed. It probably doesn't help that my screen isn't retaining its shape very well (add heat and it soon sags). We are burning 24/7 (burned 4 full cord to date this season), 18" medium-sized splits.
Regarding smell, we occasionally (rarely) have a slight smell. All gaskets are original. I suspect a clogged cat would accentuate to any smoke leaks.
We aim for higher stovetop temps (500-600), and as a result see a little higher flue temps than you are seeing. Almost always a secondaries burn going in this colder weather.
I called Woodstock with my findings and talked with the guys in the back about brainstorm I came up with to mount a small strip of stainless with screws so the screen could rest on it in the back an not gap sag with heat.
They said they would do some experimenting this week cause the holes were already there in the secondary plate to mount it to (a couple of the air holes) they said there were plenty of them so using 2-3 of them shouldn't affect anything. said they would get back to me later this week or next an that it might work.
They sure are some great people to work with, for any of the small issues I've had.
I received my new cat last friday ( warped problem ) the new one has 3 strap support legs. Looks like it should solve the problem. I dont hear the louder cat heatup pings like the single leg ones.
No smoke smell at all here either, but my draft is a++ so dont get much chance to to leak smoke smell
I burn mostly locust-oak and I do half to close the air down at a slower pace on load ups to get the load charred good for proper lower burns, compared to softer woods.
Todd2