The impression I get about the M103 is that they virtually never need a chain replacement. When I had the head off our 300TE at around 140,000km (for a head gasket and valve stem seals) I had a new chain and tensioner ready to fit. Due to no obvious difference between the new and old chain and the lack of availability of the correct chain rivetting tool I elected to fit only the new tensioner. I was reluctant to replace an original chain (with no apparent wear) with a new one joined by either an improvised rivetting technique or by a clip type joining link. That was about 3 years ago and the car has now done about 175,000km. Others please assure me that I made the right decision.

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107.023: 350SLC, 3-speed auto, icon gold, parchment MBtex (sold 2012 after 29 years ownership).
107.026: 500SLC, 4-speed auto, thistle green, green velour.
124.090: 300TE, 4-speed auto, arctic white, cream-beige MBtex.
201.028: 190E 2.3 Sportline, 5-speed manual, arctic white, blue leather.
201.028: 190E 2.3, 4-speed auto, blue-black, grey MBtex.
201.034: 190E 2.3-16, 5-speed manual, blue-black, black leather.