Some sintered copper/graphite brushes will swell upon long exposure to
moisture. You may have to distort the brush guides to get them out....
essentially, they're corrosion-welded to the guides.

I've e-mailed the guy to explain the situation and ask how he tested it.
For the reasons I gave earlier, I am almost entirely sure this is a 115
V machine, so I don't think this is the problem. I have tested it on
several different plates of various thicknesses and can hear the safety
switch clicking, so I think that is okay. I doubt I can follow Lloyd's
advice and distort the brush guides to remove the brushes as the guides
are moulded into the motor housing. Unless I can chip or tap the brushes
out, it will need a new housing, but for now I don't wish to alter the
condition of the machine. I will wait and see what the seller has to say.

Keith, I will bear you in mind if I am unable to return or repair the
machine.

Thanks for all the suggestions.

Chris