A method for getting oil off an objective is
to take a piece of expanded polystyrene (the
popcorn-like stuff used for packing), break it
in half, and place the lens against the newly
broken surface. Almost all the oil is rapidly
soaked up by the polystyrene. I got this from
a book: Light Microscopic Techniques in Biology
and Medicine by J. James; The Hague: Martinus
Nijhoff, 1976.  It works well.

                           John Kiernan.

Gary Gill  wrote:
> Regardless of the solvent used, never put it directly onto a lens surface, as it may seep around the lens circumference and loosen the cement that holds the lens in place.
> Instead, first put a drop or two of cleaner on a double thickness of lens tissue and then clean the lens.  For recessed concave surfaces of plano lenses, use a sharpened bamboo stick to press on the moistened lens tissue and move it over the lens surface.  Move to a dry area of lens tissue, and thoroughly dry the residual fluid to avoid spotting that can make the lens dirtier than it was initially.  
> Use an inverted eyepiece as a jeweler's-like loupe to inspect the lens before cleaning, so you'll know what you're dealing with, and after cleaning to confirm that you've accomplished what you intended.
 
-- 
-------------------------
John A. Kiernan
Department of Anatomy and Cell Biology
The University of Western Ontario
London,   Canada   N6A 5C1
   kiernan@uwo.ca
   http://publish.uwo.ca/~jkiernan/