Here's what I have found from owning three and working on a bunch more.
You will find badly bent recoil springs in some. I just straighten them out and they work fine. Some 'experts' swear you must buy a new spring. Not so in my experience.
I have a real old one that had a very sticky bolt. Turned out the soft cast aluminum receiver had been sent in toward the bolt under the ejection port. When you take the bolt out look inside the receiver for signs of rubbing. If so file it smooth and try to get a slightly polished surface. My most reliable 60's have around .030" slop between the receiver and bolt.
Don't use ammo that has blunt bullets like Winchester X-Pert. Won't feed right. Mine all prefer Winchester Dynapoint ammo. since Winchester seems to find it necessary to play games with Dynapoint availability and have greatly raised prices I have gone to Federal ammo.
Polishing all surfaces of the bolt seems to lengthen time between cleaning. I jewel mine because it looks cool.
I lube everything that moves with a good gun grease, Tetra, etc. except for the bolt! I run it completely dry. I've had no problems with a polished bolt galling the receiver.
Model 60 triggers are a whole 'nother subject. They can be made very nice.
Here's a pic of my favorite M60 which I'm sure you've seem before, how I keep a scope from walking off the back of the receiver and my trigger stop:


