Hey, I just bought a '91 Sierra and the cab corners and supports are rusted out, causing the rear of the cab to sag a few inches. I've heard that if it isn't fixed, it could cause the windsheild to crack. I've heard of cab corner kits to fix the visual holes but it doesn't do anything to support the cab. Right now the rear of the cab is sitting on the frame. I know most of you have either new trucks or live in a place without snow (therefore no salt to rust your truck) but if anyone has any info on this problem, it would be appreciated.