Op rod on a m1a is a straight line. Garand is like a dogs hind leg they say. Op rod on M1a is one of the big upgrades from the Garand, along with the roller on the bolt.
Many people trash the non-GI op rods on the M1A in favor of the GI. Most prefer the TRW version. I don't know if this is really necessary.
Cleaning the carbon caking out of the gas cylinder is probably a bigger deal. They sell a drill bit on a screw driver handle for that. As it cakes up it changes the volume, and barrel harmonics. So the zero will shift.
