I have a Masters Degree (with Distinction I might add
) in Corrosion Control Engineering and work as a Metallurgist for a company that makes jet engine discs and I can tell you that there is only one way to permanently solve the problem.
You have to remove ALL the rust. This would usually need to be done by bead blasting. Wet and dry will work to a point, but obviously, invisible amounts of rust are present the second you stop rubbing due to the water used.
Once rust is removed, you should then dry the area (totally force out all the moisture) - the missus back-up hair dryer can suffice, and you risks less of a beating if you knacker it.
You then need to repaint in a temperature controlled, dust-free, de-humidified room for best results. Good body shops will have such a facility. Best to use a zinc-based primer. One that contains resin as well gives a tough protection. Then paint, then laquer. You could try without the zinc-based primer, but IMHO the steel that is used on the Alfa bodywork is likely (but I have not conducted independent chemical analysis of this, so it has not been confirmed, although this can be arranged for £30) to be cheap and dirty (high S, P, Si), so you are much better off with the zinc primer to be sure.
Wax over the top of this will provide further protection, but not wax on top of rust. You are just sealing in water to the area and unless the wax is very thick, oxygen will be able to diffuse through the barrier slowly, meaning slower rusting (but still rusting).
I believe oxygen can diffuse through the paint to the rust, but this is O.K. just as long as water cannot (which it can't providing it has been put on properly). You need water (electrolyte) oxygen and metal for oxidation to occur at a sufficient rate at room temperature.
Sorry to be a tw@t
