Honestly MB sugarland are a strange bunch. Their parts sales hates me while their service dept thinks Im poor and from the moon because I drive ancient (according to their sales) MB sedans - one dressed up lady told me that my diesel benz is dead because its engine is rattling
anyway - I have seen this button and plastics deterioration and its caused by using overly caustic solutions and some solutions with petroleum distillates in them. Its not just an MB thing. And if it were heat etc. the plastics wont melt but literally crumble (try an old chevy truck)