I've ruled out (for now) the steering pump. I did a hail mary and attached some paper toweling to a bent wire, dipped it in lacquer thinner, and ran it underneath the pump. It came back looking 'sooty' but no sign of fresh oil on it.

I'd cleaned the A/C pump before taking my roughly 12 mile trip yesterday. And as mentioned, only ran the A/C for about 10 minutes. I'd cleaned it prior to driving, and this is what it looked like. About a 12" puddle on the floor underneath it.

To repeat, since I can see oil between the pulley and pump, apparently the front seal did decide to let go.

However, check out the bolt head that the red arrow is pointing to. Is there any chance that the hole for it could go all the way through the block? Once I cleaned things off, it looked like there was black around the head - similar to the small cam covers silicone.

I could undo the bolt, but should it go through (doubtful), I need to be ready to change the oil/filter.