Be very wary of rusting German tracks,even the spare ones on the front plate.

The metal that German tracks are made from has a very high (as I understand it)zinc content amongst other things resulting in them never rusting,hardly ever wearing and rarely breaking.

As to weathering then I can only relate to you my own maxims.

1/ Study as many photographs of your subject as possible.

2/Paint what you see,not what you think you see.

Mark