The M103 timing chain is very durable.
http://www.peachparts.com/shopforum/tech-help/120256-original-timing-chain-guides-record-mileage.html
What is your mileage and what is your oil consumption>?
My 88 300CE M103 taps once in a while when I start for a few seconds. I consider that par for the course for a 27 year old car with only 144,000 miles. I think it's more likely from the top end, not the chain.
Do you know if your valve stem seals and guides have ever been replaced? They won't last forever on a 103.