Does Mercedes cite a particular specification in their
service literature? I don't recall seeing one for A/C
oil.

When servicing my '87 124 system last fall, I just used
a dehydrated mineral oil for air conditioning systems,
purchased at my local McAutoParts store. It's only been
seven months, but nothing has blown up yet.

Perhaps Nippondenso publishes a specification you can
use to make a selection. After all, it's really to
compressor you are lubricating.