I have posted in the forum about screenwash reservoir damage that affects some Z3. It seems to be the ones mounted directly to the bulkhead that have the issue. There are two bulkhead mounted types 61608383541 and 61608381483 (for vehicle with headlight cleaning system) look identical but the latter has one extra hole in the tank.
I have a new 61608381483 (for vehicle with headlight cleaning system) for sale in ebay as it was purchased in error. Its on for the same price I paid £90.00, in case anyone is interested.