hi poul
i just fixed my zeiss few weeks ago.
as told in previous post, disasemble the shutter and take off the lens.
to clean the shutter and iris, i bought some iso/propylalohol , poured enough to cover the shutter in a plastic bag.
then placed it in a michrowave spectacle cleaning unit for a couple of cycles.
according to my watchmaker, propyl works better than anything else and leaves no trace of oil.
only thing is, that if shutter is soaked for more than 5-10 min, printed letters might dissolve.
ocasionally you can dismantle printed areas.
work the shutter and iris while soaked wet, dip in fresh propyl and leave to dry.
if you have to oil. only oil visible parts in the shutter sparingly.
it works for me.