Dear Susan.

For years, our Organisation has been using the following solution to clean
the oil immersion lenses of our +/- 600 microscopes with no reported ill
effects.
Mix 3 parts absolute alcohol (methanol works as well) with 7 parts ether and
store in a glass bottle with a glass stopper.
The big trick with using a solvent to clean an objective, is not to leave it
on the front of the lenses for any length of time, otherwise you run the
risk of damaging the matrix that holds the front element in place, so wipe
on and wipe off immediately!

Mike Kirby
S.A.I.M.R
Johannesburg
South Africa.