Bondo

Filling the bad slot cut with Bondo and re-routing it seems to have worked. Here is the cut I needed to repair:

I have never worked with Bondo before, but the instructions recommended only mixing a small amount at a time as it only has a 3-4 minute working time. Here is how much I was able to fill on the first round:

Here it is all Bondo’d up:

All sanded:

And with the slot recut: