I was eventually forced to resort to destructive removal of the original nuts on my W123 upper control arm. While I could find variety of 'similar' replacement nuts, I had no desire to compromise on such a critical part.
These nuts are as near to the original corrosion resistance, thread type, ISO spec, class, nut type, and physical measurements of the original available today so far as I can work out. The only potential difference I am aware of is that the original might have been protected with cadmium rather than zinc, but that seems cost prohibitive in the present day even ignoring availability.
The caveat was that, being a special order, it had minimum order of a 100 nuts and I am now left with 98 'spares'.
I figure that with the nightmare the original nuts are to get off, at least a couple others might be in the same situation. If for some wacky fun reason you actually need 100+ nuts, contact Fastenal sales directly for "M12x1.5 980V-10 YZ" and they should get you set up.
My price:
$1 a nut/$10 a dozen.
$5.15 shipping within the United States.
Paypal accepted.
Best I can tell,
Priority Mail Small Flat Rate Box is the cheapest box option for shipping, but I am open to other ideas. The likelihood of damage/loss in the mail shipping them via envelope doesn't seem worth the 25 cents it would save in postage.
While I spec'ed the nuts out for W123 upper control arm nut replacement, they are likely used elsewhere in this chassis and others. I couldn't tell you which or where.
Do be sure to put the upper control arm bolts in from the other side when you reinstall so that the bad fastener can't hurt you any more!
