Thank you. 

In 7/8'' scale (1:13.7) the 45mm. gauge would represent 36''; in what what the English call 16mm. scale (1:19), the gauge would represent one meter (39.4'': that is the reason for the existence of such an absurd scale!).

to what scale are these?

Hey Rusty man, thank you so much for your detailed and well-written reply.  As soon as the word ,,solder" came up, I knew this job wasn't going to be for me.  I'm a relic of the sixties, when my Mantua steamers and Athern diesels were easy to open up and required no (shudder) soldering.  Even my Euro-N from the 70's was still doable, as are today's J-trains.  It's like the differnce between servicing a ´67 Mustang and a (whatever) today. 

Here I couldn't even get the green shell off, despite unscrewing various screws.  I did grease the gears from underneath and that made no difference.  It's definitely the motor screeching for help.  (the engine has hardly been run, only a few minutes over two years). Your guide perfectly reinforces what I had figured from the diagram, which was that opening up that inner shell containing the gears and motor was going to be too tricky for me.

Since I live in Switzerland sending it off by mail is not an option.  We have a guy that comes into a LHS (practically the only one left) once a week to fix stuff so I'll entrust Emily to his tender, Märklin-oriented mercies.

Once again, thanks for taking the time and effort!  May this thread help others down the road!

Getting at the gears is easy but how do I get at the motor?  She is screeching something terrible.  Sounds sort of like a whistle, but never stops.  Both directions.  The exploded drawing is not much help.  Thanks in advance!