In an earlier post I thought the stains were oil. I took a closer look and I think they could be chocolate. Problem is the shirt has been through the dryer.
Did you try a Clorox Bleach Pen? How about powdered Biz? You can just mix some up in a bowl and soak the shirt overnight in it, I haven't found anything that Biz would not soak out.
try soaking it for a few hours in an oxyclean solution.
of course oxyclean works best in hot water so as hot as your shirt can tolerate.
sometimes I have to do it twice before the stain is gone