How to remove stubborn stains on housing lens

Got an odd problem. I've got a few water drop marks on the inside and outside of the lens area of my housing that must have dried on overnite (I believe its water but maybe its oil...). Despite rinsing with freshwater and trying to use some lens paper with a lot of muscle, they refuse to come out. Anyone suggest a way to remove these safely with maybe household cleaners or any specialized photo cleaning stuff?

Thanks

edit: looks like it might have been finger grease... came out with a washing with dishwashing liquid

I have the same problem on my Light and Motion macro port. An employee at Backscatter told me to use nose grease. No joke.

I didn't really work well though. Unfortunately, I think there is a point at which it is near impossible if salt deposits are allowed to harden for any length of time. Be careful about getting too aggressive with lens cleaning tissue. You might start to take off the anti-scratch coating that many housing manufacturers put on their port glass. In fact, I'm now wondering if what I thought was marks left from salt are in fact areas where the coating has been stripped away a bit when I used lens cleaner to clean ordinary smudge spots from the glass.

Nose grease?!! Never thought about that. I guess that is sold in the same area as the shark snot defogger?..lol