The Bally flippers of that era have a plastic bushing that rides inside the coil sleeve to keep the plunger centered. From your picture, it looks like that clip is dislodged and out on the spring. I can’t really tell if that EOS switch is the right length or not. If the flipper isn’t put together correctly, it’s not going to work properly. If you’ve got one side that works well, and one side that doesn’t, compare the two with respect to how it feels mechanically, when the EOS switch opens, how the coil and switches are wired, and how much play there is in the linkage.

Dave