Many thanks to all!
@WarrenD: please PM me your adress, I will send you some red plastic from my stock.
@Bo: I knew you would come around to help me, thanks a lot! This really is a great help, I studied all the photos I have but the radiatior is barely visible on almost all, not even speaking about the color. Replicas are mostly showing the radiator in greyish green, but those are still replicas...
Cheers
Ondra