Please no cleaning products . It is a mechanical issue . You either have a worn coil stop or a broken coil sleeve or your flipper coil plunger has some burring on the tip . Get a flipper rebuild kit Amd callnit a day . If you want to clean it just pull it a part and wipe as much of with a paper towel and get as much of the grim off as possible until the rebuild kit arrives .

Do NOT spray any flammable materials around a coil! Sounds like you need to rebuild the flipper. The spring could be warn out that pulls it back. The coil sleeve could be dirty. The shaft that is magnitized could be rusted and creating friction. A picture of the flipper coil would be helpful to help explain the root issue.

It looks like your EOS is bent and hitting the return spring. Straighten out the switch leaf and try again.

I sometimes find loosening the 4 screws that hold the coil to the bracket, straightening everything up and re-tightening will sometimes help similar issues I've had with flippers.

Is it OK to spray some PB Blaster lubricant into the shaft where the shaft goes into the coil (assuming that's the real problem), or is that a no-no?

Only if you want to start a fire.

no no

Like the other guys said - take it apart, put some alcohol on a q-tip and clean out the inside of the coil and coil sleeve, wipe down the plunger, check for a burr on the end of the plunger and the coil stop and file them off. Then order a flipper rebuild kit and a rubber ring kit. Clean that flipper off really good before you replace the rubber, it looks like it's been around the block a few times.

It appears possible that a set screw is impacting the end of stroke switch with return of the flipper mechanism by the spring, which could have bent that tab on the end of stroke switch and caused issues with the return spring.

The coil stop might be getting magnetised causing the plunger to stay in. Swap it with one from another flipper mech for test.

BTW the nyliner has been installed backwards at the end bracket.