What do you mix up for fuel stains? I’ve never felt mine to be very good. I use Tam Smoke with a tiny amount of Clear Red mixed.
I use oils. A little lamp black mixed with some Burnt sienna and HEAVILY thinned. I use it after I’ve done the final flat coat, that way it spreads through the flat finish more realistically.
I used diluted MM flat black here. Makes for easy realistic oil and fuel stains without having to resort to AM products.
Steve