Like any cleaning, I'd start with something gentle - try soap and water, perhaps dish detergent and see if that helps. From there, if needed, I'd escalate to window cleaner, and beyond that a citrus based cleaner. If those don't do anything, then on to isopropyl or denatured alcohol, though test those in a small area first to be sure they don't attack the handle material.
Good luck, Xcelite makes good tools.
-Pat