Oh!! Oh, I got it!
Thanks to SteveH's suggestions!
The problem was staring me in the face the whole time but I kept discounting it as just an oddity of the machine.
There are no set screws to join the hook to the shaft. It looks like a pressed on bushing or something. That whole bushing had slid back, orienting the hook too far to the right. This is why I typically don't remove old oil until I'm finished servicing! I could see exactly where it belonged and how far it had shifted.
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It was far enough left that it sewed most of the time, but something - possibly vibration or temperature caused it to shift a tiny bit to the right and Crunch!
Now that it's adjusted, the clearance between hook and needle is better and the 1/50 skipped stitches are also gone.
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I saw that clue a number of times too - the loop would sometimes form but not be far enough to the right to get grabbed by the hook. I ignored way too much here. I'll blame mild burn out for that at this time.
