Before I fabricated an alignment guide to keep the bucking bar perfectly perpendicular, I managed to nick the J-channel in a few places which left a healthy dent that was barely visible on the exterior, but definitely on the interior. I was a bit concerned that this would be a structural issue, and was prepared to drill out all the rivets and replace the channel completely. After consulting Vans however, they recommended to buff out any sharp edges and build on, so that's what I did.