The chain is not the problem. I have seen many original chains last to 300K. The problem is that the tentioner occasionally will leak down when the engine sits. During the rattling period (about 2-3 seconds)the rails which never touch the chain are banged around.
The original rails (viewed with valve covers off) are white plastic. After 60-80k they turn amber; then brown. Once they are brown they are as brittle as glass.
Have the rails checked by a color co-ordinator (bg).
Bosch Master, ASE Master, L1
33 years MB technician