filmscanners: Cleaning HP S20... Art?

["Richard Dellman" <advantage@datec.net.pg>]

After having my S20 for a year, using the blower on the glass lens isn't
enough to get rid of a visible build-up of dirt... obviously affecting
scans - yet the little manual is quite emphatic about not touching it or
using anything other than air.

I'm not sure if its glass or plastic so am worried about using any cleaning
agent.. or even a lens cleaning tissue.

I'm wondering if the warnings are just to discourage careless and rough
treatment . .and that the lens is actually robust enough to be gently
cleaned...

I know Art has a lot of experience with this scanner... I'd appreciate your
suggestions..

Richard