This is what I was going to say. Mine fell out about 6 months ago. I drove 4 hours each way to my tech in Boston to fix it. The trick with doing it your self is trying to figure out where exactly north, south east and west was with the pad and making sure it lines up exactly. I figured I should just let him handle it.......If it were only that easy. The difficulty with re-gluing a pad that has fallen out is that pads develop a seat where they contact the tonehole over time. This wouldn't be an issue except for the fact that key cups are not always perfectly centered over the tonehole which means the pad seat is generally speaking not exactly in the center of the pad. If the two circles representing the tonehole and the pad "seat" are not perfectly aligned, the pad is not going to provide the same airtight seal it had before falling out. Sometimes it is possible to carefully turn the pad in the key cup to where the seat matches the tonehole before heating the key cup to re-glue the pad, but this is often tricky and difficult to see. When repair techs have to remove and replace an existing pad for whatever reason they always make a pencil mark on the pad or resonator that marks the orientation of the pad to the keycup so it can be put back in exactly the same location.
Hear hear!Take it to a tech if you have to ask what to do here.