I used "Weathershield" Rust Coat Alkyd Paint, available at Home Hardware across the country. I found a bit of original Lister green under a fitting on the crankcase and when I cleaned it carefully it was just about exactly the same shade as the Weathershield Rust Coat 64-28 Gloss Green they sell for $10 a Litre (OK, only 946 ml). It's advertised as Urethane fortified, superiour corrosion resistance, excellent for metal and wood.
Cheap, easy, goes on smooth, always available, just like the girls I used to date.
Stan