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.
I assume you mean a "ultrasonic", not "microwave".
"Far more critical than what we know or do not know is what we do not want to know." - Eric Hoffer
If you have not found the proper screw yet and want to test it with film, use a cable release. But you have to remove the screw that covers the cable release socket on the shutter assembly, if you can find the proper screwdriver for it. (The slit is quite narrow)
Have inspected my Nettar, I believe the screw needed is a pivot screw. If you will use an ordinary screw, I think it will just lock up the linkage.
The screw cover on the cable release socket may have been introduced in the later models of the 518/16. I think on models with the anti-double X assembly. In these models, you will notice a different shutter button as the cable release socket is now incorporated like modern shutter buttons.
I have the 518/16 Novar f:4.5 with Pronto shutter, this has the later anti-double X. Based on info found on the net, circa 1955-56.
Actually, the 518/16 has two cable release sockets - one on the body release and one on the shutter housing. I was not aware of the one on the body release - I just never looked that closely, I guess. The shutter housing cable release socket can be clearly seen in this picture from Marriott's World.
In my case, when I got the 518/16, I did not notice the cable release socket in the shutter button. I was preparing to check for the accuracy of the focus and tried to take out the cover screw on the one in the shutter assembly, could not find a screwdriver to fit, then I noticed the one in the shutter release button so problem solved.
Yes, it will be simpler to find a donor unit, but the quality of these cameras are good. Unless they were exposed to the elements, they can be revived...