K.S.
Use Dawn dishwashing liquid (it's the best on grease) and a Crest Spinbrush (or other battery-powered toothbrush)to work it in. Launder in the hottest water you can. If it doesn't all come out in the first wash, do the Dawn and Spinbrush again. Don't dry the pants in the dryer until the Desitin is out. As far as the suggestion to take it to a professional dry cleaner for advice, you've just done that. My husband and I own a dry cleaners, and there are expensive chemicals in existence to break up grease, but this is what we would advise you to try. Good luck.