Rifle Gas Tube

I am familar with most firearms. I have a new sks and have a question about where to oil it.. I soaked all the pieces in mineral spirits to remove the cosmoline. and i let then dry overnight. I reasymbled the rifle cleaning the barrel then oiling it as well as adding a few drops of oil to the trigger asymbly. used an oily rag to wipe down the barrel sights and basically all metal parts. my one question is how to oil the gas tube. do i oil the piston? or do I not?..metal on metal does not appeal to me so i added a little oil.. now i wonder how much I should use...