I have a filter that shows a persistent smudge film that I can't seem to get rid off.
I tried piping hot water. I tried lens cloths. I tried glass cleaner. still I see this film.

do you think there is a way to get rid of this imperfection?
for the record: this is a hoya pro1 digital 77m pola filter.


(I know this is technically an accessory but we're talking about glass and I thought it was a better fit for the lens forum. my apologies if I was mistaken.)