The MB rule of thumb for replacing your timing chain and guides is 10 years and/or 100K miles. The chains seldom break on their own but the plastic guides become brittle, break, and drop into the chain system and cause major problems. And as long as you are going to all the trouble to replace the plastic parts you might as well put in a new chain too. They are not expensive.

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1986 560 SEL (159K miles)