I  normally make good money on those knotters, but since you're an Aggie, I'll help you out! LOL  I can't see it in the pics you sent but the tuckers (already mentioned to oil the pivots on them) are kept in 'home position' by a spring on a piece of metal that is in a slot that goes into the area where the stuffer is.  (Clear as mud?)  Hay tends to get caught under the bar and will not let the tuckers go all the way home.  Lift the bar, pluck the hay out with your finger and see if it helps.  I've had this happen once a year and in some conditions several times a day.  Email in profile if you want to call me, nine seven nine five seven one seven zero nine seven.