B.M.
Lestoil!! Any oil based stains in the laudry.. this works great! Usually I don't use it full strength (I weaken it by adding water to it because it is pretty stinky and strong)... but if you have already washed the the sweater, you may need to use it full strength. (My grandma taught me the magic of Lestoil many years ago! Love Grandmas!)
Good Luck!