The Motor does sit in the Oil Res,on bottom of Motor there is a housed ball bearing that sits on a steel thrust pad,these wear and throw the motor off central,thus creating the noise.
When the old expert takes it out,tell him to turn it over and reuse it. Let us know how you get on?
'The Man' arrived and knew what's what, My Wilson is the Older one, pre plastic end on rotor, it should have a single ball bearing in the end which is missing, I'm trying to get a Ball bearing from somewhere ? in the meanwhile I tightened the nut under the sleeve,which was loose and now it is working again,without bearing, next move is to find a Ball bearing and/or turn thrust-pad over !! Fun innit,