The quarter in question is AFAIK original. It had a small dent from the inside which had cracked obviously excessively thick body applied by a lovely previous body shop. I stripped the area down to bare metal removing around 1/8" of filler all around. It appears to me that there must have been a minor dent on this quarter panel which was "repaired", and then to stiffen the panel and eliminate oil canning they just applied excessive filler (yuck). So I'm trying to fix it properly.
Right now the panel is about perfect if I press hard from the inside. When at rest it easily oil cans in and pops back with light pressure. The oil can area is definitely centered around where the dent was (now a bit of a low spot). This panel is fairly flat with a slight curvature, and is right above a body crease. Dent was right in the dead center of the flat area.
I'm not sure if I should focus on getting all the waves out of the panel first and then work with the shrinking disk to get rid of the oil canning... or the reverse. Right now it is a bit hard to work on because it tends to pop one way or the other with the oil canning.
Appreciate the tips. I'm decently experienced at fabricating and sheet metal, but "metal bumping" is fairly new to me!