I have only ever seen this when polishing compound was not totally cleaned off at the factory. It can be quite tenacious, too. Last time I had to deal with something like this it too me several hours and multiple attacks with a clean cotton cloth to get it off. I finally resorted to white vinegar, and either that helped, or it was about to surrender anyway.
If your mixer were new, I would suspect polishing compound, but if it's labeled "Magic Mill" it must be an older model. BTW, I have not found putting something like this through the dishwasher to be of much help. Only hand cleaning has ever solved this issue for me.
Anyway. I don't think your mixer is new enough for leftover polishing compound to be the problem. I would still try polishing with a clean cloth, with the assistance of either white vinegar or Everclear to try to remove any lingering residue of whatever it is, wherever it came from.
Did you ever hear back from the importer, and was that Bread Beckers that you tried to contact? If not, I would suggest contacting Bread Beckers and asking them. Electrolux still has the stuff up for the Magic Mill, but to my knowledge they don't come in marked that way anymore, they are all Ankarsrum now and they all come through Bread Beckers before being distributed out to the retailers.
BTW - I looked at the freshloaf thread, and there was one solution listed there:
What I did is just mix together water and flour into a loose batter and let it whip at high speed for several minutes, that seemed to clean everything out and likely cost less than $1.00.
This sounds like one way to remove leftover polishing compound - but might still be worth a try for whatever is causing your problem as well. Heck, maybe add some Dawn dish detergent to the slurry for its degreasing abilities - its not like you're going to eat the stuff when you're done, LOL!