Interesting info. My 2 om617 turbos both have the same necked down capscrews that ya broke.

If this kinda thing really bothers ya, drop me a PM. I have a spare head that’s cracked...

I think I'm convinced now that the bolts I bought are the intended replacement part, so I think I'm just going to put those in and see how it goes. But thanks for the offer, and I'll keep it in mind if something goes wrong.

My mechanic is surely not remembering some things correctly, as so many 616 and 617 engines seem to have the capscrews, it seems. In his defense, his son does most of the work anymore, so he probably hasn't taken the rocker arms off a W123 diesel personally in a number of years.