Another silly mistake I made so as to keep you amused.
After having checked underneath the chassis bottom plate how to route the silicon wires Mavine developed wheel slip issues. True, the Märklin chassis is notably lighter than Regner's ... let's add some lead then. Alas, this did not seem to help ...
Not paying attention to the notches (one to accomodate movement of the sprung center axle, the other where an electrical pick-up shoe would go) I had the thing wrong way round when marking for drilling - The laugh's on me !
Track cleaning, as well, should prevent slipping. I snatched one of the scrubbing sponges (or whatever these are called) from the kitchen sink and tied it underneath a three-plank.
And a few drops of lamp oil to moisten it. (Things on hand ...)
Happy steaming !