Lordy, did someone mention timing chains?!?
As Vader says, the M116 and M117 timing chains have quite a long run and are notorious for stretch. As a preventative measure, the M117 chain should be replaced every 120-125,000 miles. If oil is changed religiously, you can probably stretch that to 150K, but I wouldn't go beyond that point or you're living on borrowed time. Tensioners should be replaced when the chain is replaced on an M116/M117, and ONLY the factory tensioner should be used.
The M116 models ("380") in the USA ONLY used a single-row chain for the first few years, and as of 1984 MB wised up and went to a double-row chain. Many US 380 models were retrofitted with double-row chains and sprockets back in the day (often after motors got grenaded), but this was a rather involved, dealer-only job and fairly expensive (at least a couple thousand dollars). There are more than a few unconverted 380s still out there with single-row chains, and in today's world it is not worth the time/effort/cost to convert them. Rather, it's a much better idea to just change the oil every few thousand miles, and religiously replace the timing chain on these single-row cars every 50-60K miles. If you do this, they will run forever. If you don't, you are living on borrowed time after 60K miles. I still see plenty of 380s (particularly the 155 HP 380SLs) out on the road. MB always had the double-row timing chain on non-US 380 models, and they had the double-row chain on all US 420 M116s too. Timing chains are cheap and it's not a horrible job to change a timing chain on an M116 or M117.
In fact, that reminds me, I need to change my timing chain on my 560SEC, as it's got around 110K miles on it....
M119s don't have the timing chain issues that the M116s/M117s did, but they should still be changed by 150K or so as a preventative measure, as they do stretch over time.
I changed the timing chain on my M104 at about 200K miles. Probably didn't need it, but seeing as the rest of the top-end was getting refreshed, it made sense and it was more or less incremental labor "while I was in there." Just needed to get the IWIS crimping tool and a Dremel to grind off a pin to separate the chain.
M103 and M104 chains are quite short and have a relatively straight run as compared to the V-8s. They don't suffer nearly the stress or stretch that the V-8s do. But still, they should be changed out when stretch is measured, or perhaps by 250K or so.
The life of a timing chain is directly proportional to how frequently the motor oil was changed.