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My apologies that you did not receive an earlier answer, and I thank you for your patience!
You were very
wise not to put the overalls in the dryer after washing, as this would have set the stain further. I am including instructions on several methods to get the stain out, below, but note that the first set of instructions apply to a fresh stain, only. Additional instructions apply to an already set stain either from washing or drying, or just being there for a while without washing.http://www.howtocleanstuff.net/how-to-remove-engine-oil-and-grease-stains/
Even though you've already washed the coveralls, I would recommend using the Dawn or other brand of super-grease cutting dishwashing liquid to rub into the stain and use a nail brush or toothbrush to help it penetrate better. However, it is very important to rinse out all the dish soap from the fabric before washing with detergent again, so you don't have overflowing suds coming out of your washing machine. Trying the pre-treating products like Shout or Tide might also do the trick.
Again, don't dry in the dryer until you're sure the stain is absolutely out of the fabric.
I wish you the best of luck and hope you are successful in removing the stain!
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