Yes ian, as allan says , the plastic wheel/flange is made from nylon, and as it wears due to contact with the track, it delaminates ,coming of in bits of string like threads, these end up wrapped around the brass axle ,which then heats it up by friction, resulting in the nylon threads melting, then compilary action comes into place, it draws up the melted nylon, and draws it into the bearings...bear with me..after use, it cools down, it sets back into a lump, in the bearings, this in turn makes it harder for the drive motor to turn the bearings/axle/wheels...which will lead directly to the motor drawing more ampage,wich eventually the main bord will not be able to cope with ,...which is when the magic smoke escapes...new main bord, new drive axle/bearings,and a new cleaning motor...how do I know, well I've rear at least 7...none of my own, mine I retired after 12 years +, after jenny treated me to a new one...