You can't teach a car to rust. (Even a Maestro
)
It's all in the breeding. Unfortunately, the heritage of the Maestro can be traced to the Allegro and Maxi - what hope have you got?
If your car isn't rusting, there are certain remedies you can try. I find removing the paint and cleansing the wound with saltwater will produce the (un)desired effect.
Nothing beats a good swim in the sea, though.
Does anyone produce a fibreglass Maestro 'shell? I sense a business opportunity!!!