Kadee coupler question

[foulrift]

Hi everyone.Finally got my layout up and running and there are not problems pulling cars through switches etc.I did add 1/2oz of weight over the trucks of each box car. I did notice a small issue with a few of the Kadee #158's.A couple of the knuckles are a little stiff and don't close after uncoupling. I checked the springs using a magnifying glass and did not see and paint (from weathering ) stuck anywhere.I did shoot some graphite lubricant into coupler pockets and the springs.Does anyone have any other ideas to keep the knuckles moving loosely?
Bob