I wouldn’t use enamels on plastics again. I’m solely using acrylics because they form a flexible skin over the figure. Enamels tend to crack, even with the acrylic undercoat.
Having said that, my original Airfix type 1 8th army (purchased 1969, painted 1977-ish) were painted in Airfix enamels and have not shed a single bit of paint! This may be down to the more robust figures, though. Later plastics have thinner weapons and more easy to bend.
More nonsense on my blog: http://battle77.blogspot.com/