Ok clearly the spring is not hitting the body. What if something else in the wheel well was causing the damage. It could only hit the threads where the spring did not block it. That would explain the spring shadow type wear pattern. A stainless braded line is very aggressive when touching aluminum. Any chance the brake lines touch at some point in the wheel travel? The brake line or some other thing that’s thin enough to fit through the coils of the spring would wear away a mark like that. The stainless brake line could lay on the spring and not cause noticeable wear on the powder coat but really tear up the body as it makes a sanding motion mostly near the bottom of the threads and sometimes one coil up.

This type of damage could happen in one race or race weekend. Maybe the banjo on the brake caliper was at a different angle for one weekend then put back in the normal orientation?

Hope you don’t mind me guessing. When I am stuck I call my Dad and we brain storm to try to figure things like this out. Mostly we think of the same things as the cause, but sometimes one of us comes up with a new idea that the other has not considered.