David what I have been using is these Preval sprayers for the small stuff. You can mix as little paint as you need. They used to be available from Carquest but now they are no longer selling them. They are available from Amazon though.
After buying a unit with a jar you only have to buy the refills. It's just like spraying with a spray bomb but you mix the paint your way and you can even use hardener. Twenty years ago I overhauled the loader cylinders on my tractor and used Allis Chalmers good quality orange and they look just as good today. When you are finished just put a bit of thinners in the jar and spray it out to clean the nozzle. Done.
Cheers
Barry
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