Though your car is a W124 chassis, I am sure it was still the same as my '83 TD. My filter is located under the filler cap for the hyd. fluid reservoir. It is a small cylinder type and is held in place by a spring/clip.

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1999 MB SL500 (110,000 mi)
2004 Volvo V70 2.5T (220,000 mi)
2014 Tesla Model S 85 (136,000 mi)
MBCA member