[cctalk] Cleaning Card Punch

Folks, I have been trying to restore a manual card punch. The type with 12 "Buttons" or "Plungers" that operate a lever which pushes a punch "pin" through a die to create a hole in a card. Its almost identical to this one:- https://www.computinghistory.org.uk/det/38019/ICL-Hand-Key-Punch-Card-Machi… so despite lots of cleaning some of the pins stick down. Does any one have any suggestions how to clean the small square slots? Any idea how the holes were made? Dave G4UGM