I did a search and what you are doing is the right thing.
http://www.ehow.com/how_5070617_remo...se-cotton.html
It was interesting to note that they suggest washing it again if the stain didn't come all the way out. I would think since you have already washed it that it is too late for the cornstarch. I have had success using Formula 409. Some of the Orange Cleaners are good degreasers.
Good luck!