Lots of good advice/tips in all the above postings......
....but to summarise....
Dont rely on Hammerite (looks good in short term)
Wayoil is good (and they do it in black aerosol)
POR-15 is better
New wishbones are better still!
Make sure they are good all the way along and all the way through.......
....finally, if you do end up selling the car, new wishbones may not make the car worth £500 more, but will make it far easier to sell
It's an acknowledged weak point on the car (due to age and material, hence the spec change to galvanised), and many people will use the fact that they haven't been changed as a haggling point (I would) to reduce the offer. If they get changed now there are 2 advantages, firstly you get a car that is less likely to end up in a hedge, secondly, when/if you come to sell, the buyer can be reasured that you have done the job properly. I'm not saying that you would, but if i looked at a car with 'tarted up' suspension parts which were not structurally sound, i would wander what else has been 'hidden' and walk away, no matter what else seemed good about it.
It was only when i actually took mine off the car that i realised how bad they had become - one seemed good on the car, the other had a small hole near the seam weld (least of the problems, but the reason i bought stainless ones). When they were both off, the 'good' one was in a shocking state in the unseen places, and probably hadn't been waxoyld because of the inaccessability, even though the rest of the arm was great.