Try Evaporust. You can buy it in a quart jug at Auto Zone. The stuff is amazing. I have been restoring all of my original fasteners, centerlink, brake calibers, steering box, shifter etc off of my 69 Z with unbelievable results. Your POP has a thin type of coating or something on it and you have the owners name on the tape which could be damaged. You may want to paint it on then rinse it off with water. I have been submerging my parts then rinsing with water.
I attached a few pics that show "after" the evaporust. Wish I had some before but they had a lot of surface rust and grime.
Good Luck