As far as I know virtually all Mercedes models built since probably the seventies if not before, use deCarbon type shocks. Unless the shocks develop a major oil leak or seize, they are okay to use and don't need to be replaced at any arbitrary time or mileage interval. They can also be replaced singly rather than pairs as is normal practice for conventional hydraulic shocks.

I've experienced both types of failures. The RF strut on my 190 lost all it's oil about ten years ago, so I replaced it with a Bistein "comfort" type, which is the OE replacement.

A Bilstein on the front of my Cosworth Vega seized, and this was evidenced by unequal front suspension movement when hitting a two wheel bump - the RF would not compress. BTW, eventhough that shock was over 20 years old, I still had the original purchase receipt and Bilstein rebuilt all four shocks under their lifetime warranty for replacement shocks.

If a shock fails you should notice some type of body motion control problem, so if the ride or handling degrades, it's time for a shock inspection, and anytime you do an undercar inspection, you should look at the shocks to see if there is any signficant oil leakage.

Duke