As was mentioned, grease your gun, and that means grease, not oil. If it slides, grease it, if it rotates, oil it. Personally, I use moly based automotive wheel bearing grease, but most any decent grease will do. The Garand has specific grease points.
https://images.google.com/imgres?imgurl=http%3A%2F%2Fi42.tinypic.com%2F2psofol.jpg&imgrefurl=http%3A%2F%2Fforums.thecmp.org%2Fshowthread.php%3Ft%3D15706%26page%3D2&docid=XljmbN0spRHBCM&tbnid=C4d-xvSmVoDWZM%3A&vet=1&w=746&h=838&source=sh%2Fx%2Fim
Also, take the op rod spring out, and measure its length. It should be at least 19 1/2" long, preferably over 20". If it is at that length(19 1/2"), or shorter, it needs to be replaced. The op rod spring does double duty, in that it deals with the bolt, and feeding the bullets up into position for the bolt to pick them up.