Door mechanism problems...HELP!!

[NAPCO ken]

'79 Suburban, front doors (non-power)...sometimes when you lock it you cannot get the lock to come back up no matter if you use the key or manually try to pull it up. Then, miraculously, I got it to come up with the key after jiggling the key...seemed like something was stuck. Another problem is sometimes the push knob on the outside (to open the door) will just push in freely and not engage anything, like it's just flopping around....then after opening the door a time or two (from the inside), it will begin engaging again and open the door. Anyone have these kinds of problems?? It's driving me nuts!! Any thoughts or cures will be appreciated!!