It's an interesting problem with the nylon washer vs. stainless washer. Originally that box bolt had a nylon washer, I'm sure from the original assembly which is indicated in the original assembly instructions. Yes, it did seem to melt a bit and even started to fall apart when I started working on it. However, after the washer peeled out in pieces from under the hex and created a small gap between the hex head and the cross tube, I was able to bash the bolt forward a few times that allowed me to free it from the cook box. I don't mind it melting a bit like the first one but I also don't want the possibility of smelly plastic for the customer. I think I'll switch to stainless like most people are doing.
How about the idea of a stainless steel washer between the cookbox and the cross bar? Any final thoughts on that or just bring it right up to the rail with no washer?