Propane torch and tongs will clean it up to spec. Top handles that hang off climbers bungies are prone to this, it's just maintenence. My 200t ran noticeably better with the screen removed.
Had saw for 2 years or so. Had noticed that it wasn't as peppy and not as strong in larger wood for last year, gradually got worse. I use the saw mainly to mark logs and light limbing so the problem really just snuck up on me. Saw doesn't spend a ton of time under high load and did lots of starting and stopping and quick cuts. Glad I looked on here though. I've never had a muffler screen stop up to my knowledge. My older saws don't have screens and if they do they are very coarse. I'll be tossing the screens in my other saws as well. I don't cut much in the summer and it is humid as all get out down here, so don't think I'll be starting any forest fires.
The screen also helps preventing anything to get into the muffler, not just out of it.
I have seen some AS members customize wider stainless steel mesh onto their saws, I think it is worth a thought (doesn't even have to be stainless steel, just a wider mesh).