Some sort of oil/grease stain, will it ever come out?

[Pocketsocks]

It's been there a while, I think I must have washed the shirt, not noticed it not come out and put it away. That's usually my staining issue, too unobservant so I never get them out quick enough, but is there a cure?

if you have washed a grease stain, it is probably set now. Before setting, a solvent such as white spirit will often get it out. For laundry, those collar-and-cuff sprays will help, but may need repeated treatments and rubbing.

Do you mean cooking oil, or car/bke oil?

You can try rubbing in a bit of flour, or talc, leaving it a while (couple of hours, maybe) and then washing. This has sometimes worked for me.

A couple of drops of washing up liquid before washing always works for me, even if I missed it the first time round.