Anything vintage would have been painted with enamel , the RAL colour chart would possible give you the current mix BUT it would not be exact if using water based paints . Were all models hand painted in those times or did "M" have spray booths for the production line . This could open up a real can of worms with different suggestions .

Cheers , Tom in Oz .

You could try using car paint.

Here's an F800/3008 I restored a couple of years ago. The loco came to me as a total wreck with the smoke deflectors crushed against the sides, one coupling rod missing, no tender and a dead motor. I stripped the paint off the shell using an old bottle of brake fluid. The respray started with a couple of coats of matte black car spray paint, then added the red lining and silvered numbers by hand with acrylics. After that I gave it a coat of clear lacquer, then another dusting of satin varnish to tone the shine down a bit:



The tender had a quick touch-up of its numbers, a new step made for the other side, then a quick dust of satin varnish so it matched the loco. The loco wheels were hand-painted after I had the chassis clean and rolling smoothly.

The BR.103 you can see behind came to me as a similar wreck, it was the Hamo version of the 3053/3054. Still not quite right as the gears on the motor bogie occasionally skip teeth and lock up, there seems to be too much side play in the axles. I'll probably solve it by buying a spare power bogie frame/gears assembly and swapping them. By that stage the only original parts will be the shell, frame, armature, magnet, and some of the glazing!

The trick is to use good quality spray paint, not cheap stuff. I use Halfords (UK chain of car parts stores) as their nozzles seem to give a finer spray pattern than most.

These older models are much easier to restore as the details were originally hand-painted, so Marklin would have arranged for them to be slightly raised on the casting to make this easier (as opposed to the 103 where I had to chase around a bit to find "DB" decals for the noses). I think I used Humbrol acrylic red and Revel acrylic silver, both applied with the finest brush I could lay hands on. Best part is that if you make a mistake you can just wash it off with water and start again, the black paint underneath will stay put.

I did find that I had to use the clear lacquer first (Halfords), then the satin varnish (old can of Games Workshop "Purity Seal"). Otherwise the red went slightly pink. You need to be careful not to overdo it as the black will turn grey.

I left the smoke deflectors off until near the end, hanging them on a piece of wire to paint them. After fitting I just put a dab of black paint on the screw heads.

Can't help on the wire, as the reverser in this was dead so I put a Lokpilot and magnet in. Given that it was such a mess to begin with I don't feel as though I've destroyed something historic, it looks original (as the Lokpilot allows you to use the chassis for a headlight return I was able to keep the original bulb setup) and runs superbly now.