It takes a wee bit of advanced metal talents to 1st avoid the warping and 2nd to remove any that's there from before. Does the warped area move in and out ("oil canned")? If it does you need to find the area that's stretched and causing the problem. You need to push the oil canned portion to where it belongs while trying to determine that bad spot, then try to hammer it back to shape. You need a hammer with a decent crown on the face and slowly work it down with a dolly on the back. If that doesn't work then you'll need to heat that area and tap it down quickly while it's hot, BUT DON'T HIT IT TOO HARD. That will make it worse and you're better off with a helper to get the torch out of the way for your hammering. Once hammered down you can cool the area with cold water. To much heat will crystallize the metal when it's cooled so you want it 'blued' and not red hot. The weight of the hammer does the work, not the force from swinging it on the panel. Don't "choke up" on the hammer handle either. Use all of the handle's length to your advantage. Our Goat 1/4s are long and relatively flat. When installing them you want someone tapping each weld as it cools down, while the "red" is going away. This will stretch the weld and remove the stresses that pulls the panel in at each weld. A small gap is required to do this right. There's 100 ways to hang a panel and most of them are right, so you need to pick the process you're most comfortable with or qualified for. The new replacements are very thin (using the same dies on metal that's .015 smaller). Forget the "GM approved" labeling too. It's still an Asian panel even though it's tagged GM.