Do you know where it is broken? Is it the internals, or the plastic casing? This German guy makes some replacement bits for the mirrors if it helps... http://www.spiegel-z3.de/index.html - you will need to use Google Chrome which will translate it automatically from Dutch German Edit: Changed language
Its the internals Gary, put the caravan on the drive and caught the mirror while squeezing past, something went snap, and the mirror arm hung down.
http://www.ebay.co.uk/itm/BMW-Z3-Wing-Mirror-Montreal-Blue-OEM-/251513039585 http://www.ebay.co.uk/itm/BMW-Genui...-Primed-Z3-Roadster-51168397040-/190704688744 http://www.ebay.co.uk/itm/BMW-Z3-Wing-Mirror-Motors-And-Seals-/271465528264