I am sorry that my photography/uploading skills are some what lacking as are my painting/restoring skills so I will try with words.

For mainly sentimental reasons my most cherished piece of Marklin kit is a Rheingold using the coaches in the 4228 set probably about twenty five years old (along with a 3618 lok). It comes out on high days and holidays only when I have the time and patience to fiddle around with the conducting couplers. Other than that it has been kept boxed on the top of a tall bookcase which with hindsight may be next to a slightly damp wall. So yesterday I noticed to my horror that the black metal concertina things between the coaches have started to show through with rust. Now before I go at things with my usual bull in a china shop approach - industrial sand blasters, grinding wheels, arc welders and etc could somebody advice a simple way to deal with this issue?

I'm not sure how easy it is, but if you can remove the part and soak it in "Evaporust", the product works quiet well. You can find it at Home Depot, car parts stores, etc. It comes in a gray rectangular bottle of various sizes.

http://www.evapo-rust.com/

The key is, after you use it, rinse the item off with water well and repaint ASAP.

-Brandon