Lubrication for Seitz sliding window runners

[master]

Hi, my Seitz S4 sliding windows (similar to S5 I think) were very stiff to slide so I cleaned out all the moss and crud in the tracks / runners and they are much better! They would probably be even better with some lubrication! and I was considering a silicon lubricant so as not to damage the rubber seals, but something that helped stop the moss growing would be fantastic.

I cant find any maintenance instructions for Seitz sliding windows - any ideas what lubricant would be best?

Many thanks