Greg,

We had this discussion in more general terms a week or so ago. The 90 degree, or any specified rotation of a specific thread pitch will give you the bolt stretch, or preload, you are looking for more accurately than torque for a bunch of reasons.

To make use of this technique the closure, meaning the fasteners, the gaskets and the pressure boundary parts all have to be designed knowing this is how the preload will be applied. So, more than just the gasket would have to be changed, most notably the bolts and possibly the washers under the bolts would have to be redesigned. Additionally, using this degrees of rotation with a known thread pitch method to apply preload offers opportunities to make the process less sensitive to precision eye-hand coordination, measuring tools and parts tolerances. And that leads to more robust assemblies, even when I do the work.

Like I said, I am not sure this is not how MB stocks repair parts for these cars, in sets or kits that bring the engine or whatever up to date when you do a job like take the head off. I no longer have a 75 model, and I don't know where all the guys on the site get the technical update bulletins describing how the designs evolve over time, so at the moment I am not really equipped to get worked up enough to worry about this. But it is something that should be determined before you start the job. Jim

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Own:
1986 Euro 190E 2.3-16 (291,000 miles),
1998 E300D TurboDiesel, 231,000 miles -purchased with 45,000,
1988 300E 5-speed 252,000 miles,
1983 240D 4-speed, purchased w/136,000, now with 222,000 miles.
2009 ML320CDI Bluetec, 89,000 miles

Owned:
1971 220D (250,000 miles plus, sold to father-in-law),
1975 240D (245,000 miles - died of body rot),
1991 350SD (176,560 miles, weakest Benz I have owned),
1999 C230 Sport (45,400 miles),
1982 240D (321,000 miles, put to sleep)