I got under the hood again and took another look at my stuck flipper.
I noticed that the back of the coil stop(brass rivet/bushing on the outer side of the stop plate?) was loose by at least a few millimeters. It definitely had some visible play whereas the two main flipper stops were solid.
I tried removing the stop but there wasn't really anything I could do with it so put it back on. I also noticed a sort of washer around the stop that was slightly bent, I'm assuming as a sort of shock absorber, and normal. Flipper is still getting stuck though. It seems like it gets stuck magnetically. Manually the assembly seems fine and it springs back on its own when the coil isn't energized. I can get the flipper to drop back the majority of the time by pressing the flipper button halfway so as to only engage the main right flipper. I'm not sure of the correlation.
I took a look at the contacts for the flipper button assembly and the spacing seems fine to me, and it is visibly separating contact at the second stage when releasing the button.
I will try replacing the stop and while I'm at it, the plunger/link assembly and nylon tube too. Hopefully that will fix it as the game is pretty much unplayable right now.