It's been my experience in a bit over forty years of using several examples that a Marlin M60 is every bit as functionally reliable as one can reasonably ask a .22 RF semiauto to be IF it is given the proper care.
Correct reassembly, as Lambo119 mentioned, is part of it. The action group on an M60 is also much more complex than those of many other rimfires, mostly due to the feed mechanism required by the tube magazine, and requires some special care to get it thoroughly clean. Flush it out thoroughly and make sure that it is dry and everything moves freely before you lube anything.
On any blow-back rimfire there's going to be a good deal of debris generated. The more moving parts there are involved in the firing cycle, the more it's likely to be adversely affected if the wrong type of lubricant, or too much of any type, grabs the crud and keeps it where it can build-up and turn to goo. IMO, this is the single most common mistake one runs into with M60s and about any other RF semiauto. On all of my several RF semiautos, especially the M60s, I use 'dry' lubes wherever possible and a 'needle' pen to keep any liquid products precisely placed and at the absolute minimum necessary. I've had very good service from Remington Rem DriLube, Hoppe's #9 Dri-Lube with teflon, Kano Dryphite, and Dri-Slide.
Pay particular attention to the extractor. It should move relatively easily and have no 'gritty' feel in it. The recess in the breech face where it rests with the bolt in-battery should also be completely clean and oil-free. I always inspect the nose of the extractor carefully for wear or damage with every cleaning.
Kept reasonably clean, properly lubed and fed with decent ammo your M60 is capable of giving you at least as high a level of functional reliability as any other RF semiauto. With its favorite load many M60s are capable of delivering a level of accuracy far above their modest price.