A couple of years back when I restored my T I ran into the same problem. What I did was clean all grease etc from the area surrounding the factory hole. Then I took some large plastic washers and used some special rubber type glue and bonded them around the hole on the inside to strengthen the area. Then, when you use the plastic fasteners from underneath, you can't tell they have been reinforced. I think I might have painted the whole thing with "bumper black" paint at the same time to freshen it up. Hope that helps.