How to clean a focusing screen?

[hexiplex]

I am in the process of selling my Rolleiflex SL66, and to increase my chances of selling the camera at not too large of a loss I want to clean the absolutely filthy focusing screen. It hasn't bothered me in practical use, but for purposes of sale, I feel like cleaning the thing is the only decent thing to do.

Is there any way to do this yourself?

EDIT: After a soak in water along with a minute drop of detergent the screen is noticeably cleaner, even a smudge that was previously entirely black is now translucent. Might go after that smudge with a tightly spun "electronics repair" Q-Tips and some optics cleaner, but for now, I am happy.

 

[John Hermanson]

I use dry compressed air and a goose feather for brushing off dust. Only the filthiest abused screen should need dunking, and then only in distilled water. I have never done this. use of any kind of solvent will ruin the surface of the screen. John

 

[Ranchu]

I use distilled water and a drop of detergent like you have. I have gone so far as to run under cool water and put dishwashing detergent directly on the screen and rub with my (clean) fingers, and rinse in distilled. No ill effects. I did ruin one with alcohol. It's deceptive, I had cleaned one with alcohol with no problem, a different one was destroyed. This is how we learn...