I joined a pinball league a couple years back and MB was the first game I played. I’d never played it before. The first ball of the first game went straight down the middle, without a chance of using my flippers. And auto save was turned off.

So I’ve been sour to MB ever since

As Lloyd said, make sure youre balls aren't magnetized. I doubt you've got a trough beat up enough to cause trouble. If you have a trough shim (https://www.marcospecialties.com/pinball-parts/03-16809) handy (or access to a 3D Printer), you can see if that helps. I was having similar issues with my original AFM, and the shim cleared it up.

Now I just need a solution to keep the shim from slowly sliding out every few games ...

Pull the bulb out and spread the wire connectors on the bulb out a bit (bend the "free" ends to the right). Not always the right answer, but it often works when I have a nonfunctioning LED.

shine a blacklight on it and see if the orange glows.

I didn't realize this was a problem on some models. Odd that the paint that's specifically reactive to UV light is destroyed by UV light.

I was disappointed in my Comet UV trough light—it wasn’t strong enough to make anything pop on my machine.

I ended up leaving mine off. Popped off too many times for me too. Cliffy uses a 3M tape for a lot of parts; not sure if adding to this one would screw up the thickness.

My first game of AFM was at Mom's in College Park too . I'm not sure if this one is the machine they had at Vuk in Bethesda. But they used to have one at Mom's a couple years ago that got me hooked (honestly, they might have moved that one to Vuk and then back to Mom's when Vuk closed).