When I take the front struts (Bora TDI) apart to install new top mounts, what's likely the best paint for the springs and shocks after I've pressure washed them.
Johnstones do a pretty good metal paint and primer - one of the best I think but as your struts and springs are likely to have a rust coat anyway, how about a spray of Waxoyl?
Failing that there's Hammerite - does nothing that it says on the tin (but dries in record time).
Unfortunately it will tend to collect grit and dust unless completely dry but there isn't a lot of treatments suitable for this area.
John
Rustoleum combi colour is very good but it’s quite expensive.
I stopped using Hammerite years ago after not being impressed with its claims of protection and the negativity from users reviews online.
I can’t see the movement you mention cracking the paint.
Have you considered pricing up new springs as they are worth doing if age is unknown.
I can't see a break in any of the springs and the all four wheel arch heights are the same.
I disconnected the bottom of rear shocks yesterday to test them and they seemed canny. Resistance up and down and when compressed, slowly extended under their own steam. I did the bounce test on all four corners and the font and back were the same so hopefully, the front shocks are canny too and I only need do the strut mounts.
The o/s is pushed up the most and presumably the cause of the occasional clunking I hear.