I heard of someone on here fixing a dented-in header with water and gave it a try last night, and it worked great. Mine was dented about half way in at the first bend, and I just filled it with water about 4 inches passed the dent and stuck it in the freezer. A few hours later I'd take it out and let the water melt, then stick it back in again. I did this 4 times and it's now difficult to tell where the big dent was. The only thing to watch out for is that you keep the flange (thing that bolts to the cylinder) held above the dented area when you stick it in the freezer. This is because as the dent pops out it may not leave the header perfectly round and the flange can be hard to slide over that part of the header. Give it a try next time.