The area right behind the stinger is the most difficult to fix/repair.
If the dent is in the middle of the pipe, the freezer trick usually works pretty good.
The area behind the stinger is "beefed" up making the freezer method a trial and error.
I have had them dented and used a small torch, heated up the area behind the stinger, and then pulled the dent out with a large phillips screwdriver, and a heavy pair of gloves<the pipe will get very hot from the torch>.
I have also cut the pipe in 1/2 with a dremmel cut off wheel, repaired the damage, and then aluminum welded the pipe back together. This is more trouble than it is worth. I just wanted to see if this could be done. If the pipe is a dual chamber pipe, there is no point in trying to cut the pipe in 1/2.
You can also make a gusset behind the stinger with JB weld to make it a little stronger.
If you are going to try the freezer trick, put a piece of fuel line on the nipple, put a small screw in the other end of the fuel line, and the fill the pipe with water, and plug the large end tightly. Lay the dented side down in the freezer. I put my pipes in baggies before I put them in the freezer. It might take two or three attempts to freeze the dent out<if it works at all>
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