Ive since had trouble with a class 16 motor also. They’re different part numbers but essentially the same size with shorter shafts. I tried removing the motor casing- impossible, as you cant get under the tabs to bend them. In a effort to get to the bottom of what was wrong i spun the old class 17 motor id replaced in my lathe and split the casing . I expected to find a dead pole on the armature but it was ok. Not much brush wear either , although the commutator did not look very circular , so may have some flat spots. Although there were some metal filings inside indicating signs of rubbing which could have been me opening the case on the lathe, I still suspect the rattling noise is caused by the armature hitting the stator magnets due to small manufacturing tolerances. Either way if youve had success from an alternative manufacturer, Im sure there are many who would appreciate knowing where to get them. Its a shame such good models are let down by bad unserviceable motors these days. For what its worth if you want to know what a smooth motor feels like - try the Hornby class 73!