Hello everybody!
Thanks again for your comments.
I made a test using Vallejo directly on the track - while it felt that it could work, the paint was very fragile - first scratch with a fingernail took the paint right off.
I was looking for a suitable spray paint and I have found a transparent plastic primer used in automotive. I applied Humbrol on top of that and that holds better. Let's give it some time now...
And I have some time now, so I decided to start painting. Here's all the stuff that had to be painted:
As you can see some parts are already primed, and some Humbrol 113 is already on. The mufflers are painted my custom-mixed rust.
On the photo above there's preshading done with Humbrol 113. There's hairspray and salt on the mufflers - this is about the only opportunity for me to try some serious chipping on an OD - painted vehicle!
And finally a layed of OD - here I traditionally use Humbrol 66. With some future on top of that the color is almost exactly spot on:
OK, so there will be some more weathering, a was ad maybe some streaks.
Thanks for looking and have a nice day
Paweł