Re: Roof patch causing warp / oil canning
The areas that didn't clean up with a wire brush need to be sandblasted to get rust out of the pits. An inexpensive spot blaster would be a good option for small areas if you don't already have a blaster. Then use epoxy to coat everything. Por15 or similar "paint over rust" products don't convert/kill the deep rust, and that looks like there will be some deeply rusted pits that'll show up when blasted.
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