I'm surprised to see there's a thread for this issue. I have the same problem with mine, I only noticed it 18 months ago maybe and I blamed the damp weather for that. The side panel are sticky, so are the fader (I think it got better for the later after cleaning it with alcohol).
@locosynth Not sure if you're gonna read that, but what do you mean by removing the rubber part? Do you mean the whole 0.5 cm layer?
Anyway, it really sucks that this is a common aging issue...