I had read some solutions for this problem all based on “sandpaper”. As I didn´t like it I tried using isopropilic alcohol. The problem was how to apply it. May be it is already reported, but I haven´t read it. Just in case I make an small description of my procedure. ¡¡ It works every time!!. Three keys in my HP-67
Take a piece of thin cloth and cut a 5mm x 30 mm. strip. Slide it under the springy metal's stretched area. Do it pushing with the screwdriver, slowly, be patient, it takes time. When you see it going out pull it with small tweezers. Impregnate the outside cloth with isopropilic alcohol (I used an small paintbrush to apply it to the cloth). Press the key metal down to some degree in the center (but not hard, just enough to catch the cloth) and make several passes. Flip the cloth over.
I hope it can help to somebody
Jon