At 87K miles it is time for a chain, tensioner and upper guides replacement at least, as the guides get brittle and breakup causing havoc and expensive heads and valves repair.
With that mileage there is chain stretch causing chain slap and camshaft timing misalignment. An average estimate for above job would be in the region of $2300.00 parts + labour with a MB specialist shop. Around $350.00 parts if you can do it yourself.
Or $4000.00 if sprockets and lower guides are also replaced as it involves removing the engine from the car.

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