I avoid cleaning unless I have to and use zeiss glasses wipes when I do and don’t rub hard. Seem to clean smears off and are cheap (glasses and phone screens get dirty far quicker than optics tend to). Avoid dousing in water or solvents unless you’re sure they won’t penetrate in or damage the paint (eg acetone).
Thought Bills favourite cleaning recipe was a mix of ammonia and rubbing alcohol?(“windex”)
Mayday, Mayday. I ONLY recommend the 1930's WINDEX GLASS CLEANER! The new Windex has so many other things in it, I cannot recommend it. It may be a great "all-purpose" cleaner, But I have heard that is not nearly as good for optics as the original!