I think you'll find the breackdown exemption is only for vehicles used exclusivley as breackdown vehicles.
Besdies with her age, the test will proably do the candles light? and are any bits falling off?
No it's Heliops' excuse why he never does the cooking! :-D
Another problem with an MVt might be insurance. Bear in mind public autority vehicles and EMS vehicles are usually bonded.
If the vehicle weight is under 2.5 tons, Green Flag are quite hapy to cover MV's. I have their any vehicle policy £120 a year, they have got me out of some nasty scrapes over the years.
Be almost a shame to put a body on it.
As for the hot oil trick, ehemm it's been mentioned several times on this forum. A better mixture is old gear oil heated with disiel, stinks but moves almost anything.
I've been getting very good results with Dulux Metalsheild latley. They do there own primer/undercoat and the paint can be mixed to your colour specc, in gloss or eggshell.