i just bought a used magic mill 9000 the other day and immediately put it to use making the apple walnut bread from this site, it was freaking delicious.  however,  i did find that the kneading roller would not hold to the rim of the bowl which is what causes it to rotate.  if any one feels their tension arm is not tight enough i have found it very easy to fix.  you will need two 8mm 1.25 thread twist nuts.  if you take the locking knob off the threaded shaft you can put the two nuts on, just until they are both on the shaft but not much further (rotating the arm toward the inside will expose more shaft threads).  use two wrenches to tighten the nuts together then put a wrench on the back nut and turn counter clockwise, the shaft should back out.  once the shaft is out i rotated the tension arm 1 revolution and put the threaded shaft back in place.  a note here,  when i first rotated the tension arm it acted as though it was rising up from the body and the holes didn't line up, this was just the increased tension on the inner spring, push down on the handle and the hole will line up again.  this will make sense once you get into it, it really was simple.