Wotto,
Not sure whether aluminium would be any better. I've read that a few people in the US manufactured replacments out of Delrin.
http://iobium.com/funhouse_plunger_plastics.htmI'm in the process of rebuilding mine. I've only replaced what I have to (couple of pieces) in the nylon but if it needs redoing I would go the Delrin.
Someone had covered mine in grease (internals) so have come out like new from the tumbler.
