HELP! Why do my dark knit shirts, golf type shirts, come out of the laundry with dark “oil” type stains?

you probably left some sort of pen or something similar in one of the pockets. there’s no reason for those shirts to be stained from other shirts…

don’t know if your doing this but i have been told that some fabric softeners can have this spotting effect.

If it looks similar to a transparent cooking oil stain rather than a black engine oil stain, it’s probably your fabric softener. Sometimes that happens, esp with certain colors.
Just rub the spot with some bar soap ( I think Ivory works best, but just anything basic, really) and re-wash.

I guess you most likely use liquid laundry detergent. This could be the cause of your oil stains

I had this problem for few weeks and I solved it by changing liquid detergent to powder.