Replace the buffer and the action springs thenWell this is a perfect spot to start! I do have a marlin 60 with feed issue's. I cleaned the crap out of it, not a spot of residue left in or on it and it was bad so put it all back together and nope still won't cycle all the rounds. If the shell is in the chamber it will not pick it up so the left extactor looked alittle worn so I replaced that I can't see what it's doing with dummy rounds cause it will cycle fine slow or as fast as I can open and close it but when I shoot it will jam. I wish it would do it when I manualy cycle it with my dummy's but don't and I learned the hard way with live rounds (getting brass dug out of an eye will teach you that u are an idiot)! Try'd 3 different brands still does it so now what? I could replace the ejection spring and possibly the recoil buffer does look alittle beat up but it cycles fine manually. Any input will help cause as you all said most of the time a good cleaning solves most issues.
Pull the trigger return spring out and replace it w a good thick ink pen spring. Then take a ball off a dog tag chain amd put it in the hole on the bottom side of the sear then put the spring back in on top of it and reassemble it. Most people on here already knows that trick already. There's actually a thread/sticky on it.That would be appreciated! I would think more than just me would be interested in that one. And since it's already apart it would be a good time to try it. Thanks