I disconnect the cables at the handle bars and punch a hole through a zip lock bag and push the cables through the hole. Tape the bag at the hole around the cables to seal it. Hang the bag/cables up straight somehow and fill the bag with oil, I usually use whatever I have in the garage, let sit for awhile. Helps if you can fully remove the cables or disconnect the other end to catch the oil with another bag. After sitting all night it will flow through the cables and be at the other end. I try to do this once a year. I will also hit them with some spray penetrating lubricant every now and again when I think of it.