Over 10 to 15 years of sitting some lubricants turn into an amber sticky goo. WD-40 is a common lubricant that ages to sludge. That would retard what should be the cylinder stop's quick snap back up. I'd start by removing the cylinder stop and cleaning it, its spring and the the area they work in with a gun oil like Hoppe's or Rem oil. A new spring would be inexpensive and couldn't hurt.
I hope the problem is that simple.
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