Good question, ask ten different people, get ten different answers. According to Mercedes you should replace the timing chain every 50K miles. Some people say even longer, others say less. Even still some say a timing chain never needs to be replaced. I feel inline with Mercedes. I think 50K miles is a little early, but I would rather replace it before it starts to fatique. I recently replaced mine (with the updated tensioner), I will replace the chain in about 50K miles.
By the way, did you replace the front engine cover (which includes an updated oil pump) with the new updated one when you did the timing chain? It has been updated four times and is important to replace because, the old one did not get enough oil to the timing chain. That will cause your timing chain to fail before 50K miles. The new front engine cover and oil pump get a lot more oil to the timing chain.

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Adrian Eckenrod
MBCA, PCA, BMWCCA & SCCA* member
86 190 2.3-16
83 944 ITS Racer