There is a glaziers glass cleaner under various brands. The one I've got is called 'Nilglas Nilco Glass Cleaner' in a polythene squirty bottle. Made by Bluecol. Very effective even on very dirty old glass but a bit fierce on paintwork - a bit like sugar soap. Decorators paint that is, is ok on car body work. Try glazier, glass supplier or motor factor.
cheers
Jacob