Success! I looked closer at the entire "wheel" mechanism and realized that it was simply held on by 4 screws. I disconnected the wiring connectors, removed the 4 screws, and boom, the whole unit easily came off the bottom side of the playfield. I was able to get a closer look at everything and noticed a couple more metal rings and wiper blades way in the center of the wheel. Almost impossible to see them without the unit off. I put a little super lube on those and the squealing went away instantly. Nice and quiet now.
I cleaned up the inside of the window with Novus 1 and it's clean and clear now. It had a fine layer of dust/dirt that made it look tinted before the cleaning. Looks great!
Added bonus from taking it off and cleaning everything: When I put it back in and reattached everything, I noticed that the wheel actually worked better overall. I knew it would be quieter and look nicer, but was surprised to find out it was malfunctioning slightly the whole time without me noticing. Previously, whenever the wheel would spin, regardless of where the ball ended up, the game would simply continue spelling the word "GOPHER" in reverse sequence. So if no letters were lit, and you landed on "P" the game would say you got "R" and light it up. If you then spun the wheel again and it landed on "G", it would award you "E". It would continue like that, ignoring whatever letter you actually landed on and simply awarding you R-E-H-P-O-G.
I thought this was because it was set on some sort of "easy" mode in the settings. Apparently not, because after the cleaning and reconnect of everything, the wheel now perfectly registers the letters you land on. Always nice when you fix something you didn't realize was not functioning properly while working on something else.
Back to more cleaning. Thanks all for the help. I'm sure I'll have some more questions, as this is my first 90's era DMD.