Hello i have tryed many things like wd-40 3-in-one oil ect.I found Aero Kroil to work the best tho. It sprays on so i get q-tip wet with it and put on cap! Let it soak a day or to keep it wet.It should free up then clean with toothbrush and spray a good electronics parts cleaner on it. A bit of oil on ends should do it.Be careful not to put to much oil on it! Aero Kroil can be found at Kanolabs. Use google to find it
Hope this helps! See you Afvel