If you are just wanting to clean the inside to make good connections the cleaning sticks work pretty well, they are like round sandpaper with just the right amount of grit. Doing more than one or two by hand will get to you though. I chuck mine into my cordless variable speed drill and hit every socket. Let it spin for 2 seconds or so making sure it hits the bottom and around the sides. If a socket still gives me trouble I will move the wire on the tab to the nipple and also make sure the connection to the base is solid. Of all the pinball machines I have gone through I’ve only had to replace a handful of sockets. Mind you, I am not trying to make them brand new, just reliable player machines. Have never had to go back in and fix any sockets so this method works well for me.