...you really do not need to clean it. Those tiny water
condensation, spot, or pit like things that you can only see at a
45 degrees angle will probably never affect your images.
This even goes for the rear element as well. I also used to be
really concerned over those lint or tiny dust like things inside
the lens. You know, everytime you look through your naked lens
against the light. Yeah! Those. They will also never affect your
beautiful pictures.
It's always more trouble as you try to clean those tiny spots, then
create swirls or streaks. Next you get frustrated and apply more
force. Now we're literally pressing down on the glass, and half
the coating is lifted off. ARGH!!!
Kiddin's aside, the thing that does affect your pictures is your
CCD on digital cameras. Unfortunately, for our D-SLR's, we must
clean the sensor filter. Oh well.
Paul