I have a 2000 Jeep Wrangler Sport. It has a shield under the vehicle I guess to protect the underside from rocks etc. The guy who works on my jeep said he could not get the shield off since one of the bolts would just spin. He thought there must be a nut welded inside the frame that has come loose and so he cannot undo it. Has anyone ever had that happen? What is the fix for that?