I'm not sure if this problem is unique to me or not, but the top grate on my 18" WSM doesn't seem to be quite big enough. It seems like it is 1/8"-1/4" too small to fit on the brackets properly. This is a bit of a problem as if I shift the grate too much during a cook, it can slip off and the grate will fall down. I had it happen with a couple of chickens a while back and almost lost a 20lb turkey yesterday. I cant just bend them out as the bolts are too far up. The bottom grate is fine. I am not sure if it is an issue with the cooker being out of round, but I wouldn't know how to fix that either.
Anyway, just wondering if anyone else has seen this before or if there is a suggested fix.