I thoroughly gave it a deep scrub with cold water first with dishwashing liquid, gave it a few more scrub and then soaked it overnight with laundry detergent and the stains did not disappear, any advice on what I did or what I need to use for getting rid of tough old stains? Thank you in advance.
oooo, thats not good, looks like the material was bleached somehow, like it has a bunch of light spots. For oil oxyclean spray works very well, dawn dish soap does too, baking soda can work, whatever you do dont heat dry the hat or the stains will set. I have a shirt with a couple of oil stains I treat before washing and dont heat dry and months later its finally lightening. If those are light spots, there really isnt anything you can do about that. Synthetic material is easier to clean oil out of than natural material. Unfortunately if you took dishwashing detergent to it and soaked in laundry detergent it might not ever come out.