The area where the AD rear fender bolts to the running boards is often damaged because of the stresses present there. This is a prime candidate for using lead instead of plastic to fill minor low spots. Here are a few pictures of a repair that I made to the right fender in that area.
http://www.pbase.com/dennygraham/body_work You may be heating the metal to much if your burning up an acid brush. You only need to get the area up to a round 350° to work the solder. I prep the area with a product called “Tins-tyter” tinning fluid, it’s made by the R.E.Montgomery Co., Lombard, Illinois. I’m not sure if it is available anymore. Then I use a tinning butter, which I believe Eastwood carries this contains lead. I use a clean cotton rag to apply the tinning compounds.
If it is not a highly stressed area and all you need to do is level the surface I would suggest using the plastic fillers that if properly applied bond quite well and are much easier to work with.
Denny Graham
Sandwich, IL
