The 100K mile replacement recommendation is for the M116 and M117 V8s,
_________________________________________________________________
The rule of thumb on these engines is 100K miles or ten years time, whichever comes first. The chains seldom fail but the plastic chain rail guides get brittle after time and and break dropping into the chain and causing the chain to jump time resulting in severe engine damage. Be sure to replace those plastic pieces whenever doing a chain replacement.

__________________
1986 560 SEL (159K miles)