161a Searchlight on 6 wheel Lorry (1939-41)

Hello all, part of my Mobile Anti-Aircraft Unit is the Lorry with Searchlight example below. As you can see it's a fair example. Besides the flat tyres, the fatigue on some places and the nasty stain on the back (and another place on the other side) it is a nice survivor of the pre-war period.For a long time it kept me wondering, however, what has caused the stain and what it is exactly. Why brownish red? It looks like rust. But zamac (or possibly lead) cannot rust. There is also some white substantion, which I could not identify. Everything seems to be stable, so I did not really worry, but I would like to know if others have seen the same odd rust-like stains on their models. Now there is an additional fact. You can see that the main casting seems to be fatigue-less. And it is!Some months ago I asked an expert colleague of mine, specialized in restoration and care of metals. His first routine action was to hold a magnet with it. And it sticked! So Dinkies do not always seem to have been made of zamak. In fact iron, or a lot of iron is the component metal of this model. May be some lead too, because of the white corrosion. So, besides studying your Dinky collection on the same reddish stains, I would like to challenge you to test some of your models with a magnet!Kind regards, Jan Werner