I know this will sound wild but I read it in Popular Mechanics, take some Coca-cola and pour it on there and let it soak a bit. The acid and other chemicals in the coke will actually get in the cracks and eat away the grit and grease in there. Then clean up afterwards and soak in WD-40 over night.

Lastly, if you just can't get this done local you could send them to Topline in California and have it done and/or buy some used one(s) from them to save on two-way shipping.