Were the archives focusing more on the V-8 engines? The "Rattle of Death" can indicate a stretched chain in the bigger engines, but I think the timing chain in the M103 is fairly short and doesn't bend around everywhere. It seems like an unlikely source to me.
Have someone else start it with the hood open so that you can try to isolate the area that it's coming from.
1988 560SL Black/Palomino
1988 300SEL Black Pearl/Burgandy
1984 500SEC Anthracite Grey/Palomino