Even if the bolt is messed up, you have the bolt from the other motor mount stay as a reference.
If the bolt isn't good, it should also be replaced, obviously.
Personally, I wouldn't use wd40, but I have cutting fluid readily available. If I didn't have the right shit, I'd use wd40 before I used vegetable oil because anything is better than nothing along that line of thinking.
Depending on your ability and how comfortable you are you will have to decide the position the hole is at for tapping. I would be afraid to it on the ground in the dark, but I've tapped hundreds of holes. No step for a stepper there. But do what you're comfortable with.
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