Rick Hunter blathered on in Leaky roof:

It 'might' be a good idea to have a chat to the service people at
BMW.
That's because the problem appears related to a seal - which will have
happened to virtually all the Z3's. That seal, or seals, might by some
massive fluke be a cheap part. And yes, you're dead right not to trust
your dealer. There is the fact that if the parts in question are there,
they'll be there because owners have refused point blank to pay the
extortionist prices for the 'correct' repairs, and gone elsewhere. The
dealer won't tell you where the elsewhere is, of course, unless he's on
a slice of the action.
Anyhow, the correct little mounded rubber parts should be in stock -
because it's most likely worn due to the massive scuttle shake so
prevalent in those machines;-)  
Either way, you'll get a (sort of) free coffee at the dealers - which
you likely won't get at the upholsterers. And they won't have the
correct parts unless they've got busy in the Cherman aftermarket.

--

Toby