Mix a solution of 1/3rd Mercon Dexron Automatic Transmission Fluid, 1/3rd mineral spirits and 1/3 diesel fuel. Scrub bore down well and leave it wet with this mixture. I have tested it for 14 months on a rifle stored muzzle down and it is still wet. Won't get thick in cold weather till about arctic temps are reached. The US name for this is Ed's Red. The full ER formula has acetone in it but I left it out as it can be absorbed through skin. I make it up using two quarts of each at a time and have it in various places in my shop etc. I put it in spray bottles and also have tilt top bottles so I can apply drops here and there.