Been playing (and cleaning) keys all my life -- piano, organ, accordion, calliope, etc. Keyboards get dirty and greasey with use. Light detergent, ammonia or vinegar solution have all worked for me. Mostly it takes patience to sit there and clean. I know this is old-fashioned but I work in entertainment and take the time to maintain my instruments.
I stay far away from any manufactured product that claims to "cut grease" because I don't know what else it's cutting.
Busch Gardens -Wmsburg, VA