DIY cleaning of stain from lens glass?

I was looking at buying a used old Wollensak 90mm f6.8 lens.The shutter is working well, but I notice that between

the back two elements there seems to be a light haze that looks sort of like a water stain,but it is only visible when

you hold the lens at an angle.

The last element in the Wollensak is held in place by a brass retaining ring. I believe that the way the lens is

designed, the retaining ring could be removed and the tiny lens element could be lifted out to be cleaned.

If I am able to disassemble easily(presuming I can reassemble and center lens element),is there any way to clean

the light stain off of the glass (I have a feeling that just lens cleaner and tissue will not get the job done)?

Hi !

Well you may make more bad than good.

If the rear element is a cemented pair, the haze could be the "glue" having chnaged it's properties with age.

If the haze is some sort of dirt on a plain coated lens, you may remove the coating, totally if you're lucky, partially if unlucky. (old coatings are less hard than modern ones, and the one that where designed not to be touched are softer than the external front and rear lenses one).

So I would unscrew the rear element, without disaembling it, gently rub off the dust with a camel hair brush and re screw it in place. If you're lucky you'll have removed the fine dust which has settlet on it during age. If not, you will still be able to use the lens ;-)