Use automobile paint polishing compound. It will remove the yellow oxidation in the paint and your Yellowtron will once more look like a Mellotron.
In a message dated 5/10/2009 12:33:12 P.M. Eastern Daylight Time, tomdcour@amnh.org writes:
I always used Testor's white enamel- it aged in a similar way to the
original paint but they've changed it . I know that epoxy was used from
the factory and you could get some white pigment and mix it with the very
clear slow drying type for touch ups. Epoxy yellows with time.