i took out my metz yesterday after storing in dricabi for about 8 years.
still works like brand new.however, the 'whiteness' of the flash i've yet to determine and i dunno how to 'test' it lah.:dunno:
turn the flash to full power shoot a 100% black reflective paper (actually black plastic bag is better). send to the lab ask them not to do any adjustment. if the photo turn out white your flash is as good as new.