Quote History Quoted:
Try a drop or two of oil and try to work it with a punch or paper clip.
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Above to start with,
Hence detent pin is retained by a roll pin, but roll pin is in a blind channel, so getting the roll pin out so you can remove the detent and spring to clean them, and the channel, can be a PITA instead.
So attack plan if you are trying to remove the roll pin, small drill to drill the ID of the roll pin for its lenght to lessen it spring tension to channel and open up the center of it a bit, then small threading tap, to tap the center of roll pin without expanding it and blocks channel, then use the tap or long screw to pull it out of the detent as you catch the detent and spring.
As for best guess of the problem, roll pin channel burs into the main detent channel that is binding up the detent.