If you put washing up liquid on the stain before you put it in the washing machine the stain should disappear. I use washing up liquid on most stains before putting them in the washer. With my 3 kids dirt, blackcurrant, grease etc-it gets most stains out. Hope it helps.
Cover the entire grease spot with liquid dish detergent and gently work detergent into grease. You will instantly see it dissolve. Rinse the area with white vinegar to remove all of the detergent. Wash as usual. For really stubborn grease stains, keep repeat the process a couple times.
I have found a wonderful little product, i had blue tack stuck to my carpet and no matter what i did i couldn't remove it. Then i found De-Solv- It, it's brilliant and works on grease too.