2.5 is a guess...that's ABOUT how much I ended up adding to bring it back to level. I would say it definitely wasnt more that 3.5... It never lost pressure. Neither did the 300CD for that matter, it just ended up a couple quarts low. The bolt that went missing is just a short 13mm hex on the right front of the engine, just above the oil pan - I replaced it with one pulled from a 240. While the engine was running, smoke and oil spurted out of the threaded hole. Took me a while to find an only did with the motor running because the radiator fan spread it all over the place. It's pretty sad that a tiny little bolt like that can rattle loose and cause catastrophic engine issues. In any case the problem is what it is and I want to fix it if at all possible. With all due respect I'd like to get an understanding of what it would take to do that rather that being attempted to be talked out of it.

Earlier 60's/70's 615's are quite different, I don't know if the parts I need are the same but all he manifolds and other components are very different. The only W123 615's in the country are imports of a car rarely imported.

The 617 I don't care about as much - I am thinking of swapping a 5.6L M117 into that chassis...But it would be a great learning project and a spare 617 turbo is never a bad thing.