@thomasfuchs I've had success using washi tape to remove the stickiness, at least temporarily.
I've done this mostly with Nikon film cameras: I cover the sticky regions with black washi tape (3M makes good black ones that match the tone almost exactly) and keep using the device with it on. After a few weeks to a few months, I'll take the tape off and the stickiness will be completely gone, without changing the appearance of the plastic at all.