I just repaired electric toothbrush. Again, for the third time (with different toothbrushes in my family, fuck Philips).
After two years of usage rubber button lost sealing. So replace it with screw furniture cap and seal ot with thermal-shrink tube (40/20 mm). Using only home hairdryer.
In my family it was other bits that broke. The oldest one which I believe has to be between 12 and 15 years old now still works fine though.