If you have pop bumpers that stick and you know it is not mechanical issue
as you just cleaned or electrical problem as coil is not locked on and you
are scratching your head. This may help.
Get yourself a bulk VHS tape eraser. These are likely to be very cheap at
flea markets, or electronic surplus stores as who uses VHS anymore. With
the bulk eraser not only can you verify that you have a residual magnetic
problem but you can also use it to demagnetize the parts. Usually the coil
stop and plunger. Get the pop bumper to stick then with the bulk eraser 6"
or so away just pulse the switch on the eraser. As soon as you do the pop
bumper will relax to normal position. If this happens you know that you
have a residual magnetic problem. You can even do this without taking off
the playfield glass.
If you verify residual magnetic problem, you can do this:
Take pop bumper apart then with the tape eraser turned on slowly move the
part(s) each part individually and slowly through the magnetic field. Do
this several times turning parts 90 each pass.
I have also heard you can use a TV degaussing coil as well with same or
better results. I have not tried this.
I have used this technique on Gottlieb Black Hole and a Midway baseball
machine (diagnose only) and both times has shown magnetic issue quickly.
Worth a shot instead of purchasing all new parts.
The 3rd sin of pinball IMO is having sticking bumpers the 1st being a
flipper with a problem, the 2nd being a dirty playfield. : )