Are you talking Tcut? This is primarily designed for paintwork as it takes a very small amount of there top coat off to reduce scratches. It will probably do the same for plastic so should be OK but again, it is applied with a ":damp" cloth so water ingress should be watched!
As I said earlier, if it's the top shell that is b ad then remove it, quite easy, and wash it in a sink with warm soapy water!