Same thing happens with a somewhat expensive musical instrument brand that keeps using that plastic for their buttons.
As far as I can tell, it breaks down slower the more you use it, must be interacting with oils/something from human fingers, as I only have that happen for things that remain in storage for months/years at a time, but the gear with that sort of plastic that I use every day/week doesn't have that happening.
Yeah I had an official silicone iPhone case that was being used for about 8 months, replaced it with a third party leather one about a month ago and already within that time I noticed that the original one has gone all slimy just like those old plastics. There must be something about using it day to day that keeps it from breaking down.
As far as I can tell, it breaks down slower the more you use it, must be interacting with oils/something from human fingers, as I only have that happen for things that remain in storage for months/years at a time, but the gear with that sort of plastic that I use every day/week doesn't have that happening.