Black hands of tinkering with car motorcycle moped or bicycle? Grab coffee and a little oil (sunflower or lettuce) rub.Then wash them with soap and they will be clean.
Oil slicks we treat it like any other stains. An oil slick on a page of a book we deal with ether. Before we begin treatment, we lay beneath the stained page a piece of glass or other material that prevents the stain continues on the next page. The gray-paper-ironing method is old, but very effective. Linseed oil stains get away with hot soda water.
My husband had in his sweater a salad oil stain of 50x50cm. I thought the sweater was lost, but I have a booklet with old household tips. Here is that you have to wash the stain with alcohol and salt. I have this stain treated first by hand and then put in water with salt and alcohol after an hour just is machine washable. To my surprise, the entire stain is gone out. You'll never see it again.