Ron Pyke , Dec 08, 2009; 12:43 a.m.
Try good old fashioned cleaning methods... blow the surface clean with a rocket blower or some such, then use lens papers and cleaning fluid (gently)... the modern lens cloths work well too. Make sure your cleaning fluid is safe for coated lenses - optometrists often sell suitable cleaner if your local 'big box' electronics store doesn't have anything suitable.
This worked for one of my old OMs.
Good luck! It is a great lens.