I have a perspex canopy over an outdoor swimming pool. It is 10-15 years old and in generally good condition apart from several large areas, several feet square, where what appears to be sunscreen cream has clouded the plastic, rendering it white and opaque. It will not wipe off with a damp cloth nor rub off with a fingernail. Does anyone know of a restoration treatment suitable for this which is over a larger than average area, i.e. not suitable for small cleaning kits? Thanks!