Timing chain, guides and tensioner on the M116/M117 V8 — an age job

The single-row timing chain, plastic guide rails, tensioner and cam oiler tube on the V8 engines are the community's number-one mechanical worry, and are considered due by age (roughly 80-100k miles or every 10-15 years), not just mileage, because the plastic parts embrittle and can cause catastrophic failure. Estimates cluster around $3,000 for chain/guides/seals, though a minority argue a genuinely low-mile car with a quiet chain is best left alone.