This will give you the look of fuel stains on any type of engine or metal object.
This enamel-based paint just needs to be painted on.
Apply with a brush in different layers of different intensities for the most realistic effects.
Instructions are not included but I have a free downloadable PDF file combining a few AK Interactive 'How-to use Product Guides' (specific to this weathering set).
I also have a fine tip Tamiya weathering brush and a medium tip brush.
One 35 ml-bottle, by AK Interactive.