A former technician from the 'Oude Delft' told me that the best 'liquid' to clean lens-surfaces was spit (yes the mouth-water). Spit has enzymes in it that solutes dirt and micro organisms. Just keep the lens-part (the glass) in your mouth (cheek) for about 10 min. Then you can clean the lens with any 'chemical' you find suitable.
If you, by accident, happens to swallow the lens-part, it will come out the other end a few days later and the dirt and nicro organisms will be gone too...

Be careful when reassembling and aligning the optical elements.