There is a grease spot remover you can purchase at fabric and quilt shops. I get it at the Hancocks in my town (not the same as the Hancocks in Paducah). It's made by Sullivan, is called Spot Remover. You spray it on, it dries white where the spot is. After it dries, you can shake or brush it off, or wash/wipe gently with a damp cloth. Works fabulously. I use it when my husband drips butter on his shirts and ties.
I found the stuff years ago when I worked at a company that made knit items such as cheerleading uniforms. Often times the knits would brush up against the knitting machinery, which would then leave grease spots. We'd spray this on, blow it off with compressed air after it dried, and you could not tell there had ever been anything there.