Hello Tom, I sure wish I could shed lite on this problem as I have this exact problem on my 2008 Knight. I've had the problem for over a year now and haven't been able to figure out the problem. The amount of flakes that blow through has decreased quite a bit but there are still a few small flakes that blow out. I really can't tell if this problem is affecting my cab ac air flow or not. Overall, my cab ac only rates about a 'C' grade. I'll sure be interested to see if someone else has a fix for this problem. Thanks,
Jim Bradley
2008 Knight, 38PDQ