Bilstein or Sachs shocks (the OEM ones on Benz) are always high pressure nitrogen compensated, meaning that there is a separate piston in the bottom (or top in the case of older F&S shocks) that keeps the oil under pressure and prevents air getting in as the fluid slowly creeps out of the piston seal. The result is very long life as you never get air in the operating part.

What happens instead is that the rod piston eventually starts to hit the compensating piston as it rises from fluid loss. This causes the car to ride VERY hard and the shocks to knock badly. This is when you know they need to be replaced.

KYB are similar, but they don't last as long and are somewhat harder than Bilstein HD shocks, so you may not be happy with them.

Both my W124 chassis cars have the original shocks and struts, both have more than 200,000 miles. Ditto on my brother's W126. I put a pair of used Bilsteins from a 1967 230S on the 280 SE, rides like new.

Don't bother to replace them unless you have typical "bad shock" ride, tire wear attributable to bad shocks, or they knock too much.

Peter

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1972 220D ?? miles
1988 300E 200,012
1987 300D Turbo killed 9/25/07, 275,000 miles
1985 Volvo 740 GLE Turobodiesel 218,000
1972 280 SE 4.5 165, 000 - It runs!