My W124 300E leaked coolant for a day then stopped for a week before starting again.
My leak was coming from the o-ring between the pump and the block but as the car had done 260000kms, I put a new pump on anyway.
Took me just under 2 hours including a trip to the hardware store for some rubber grease.

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Tony
76 W116 280SE
74 W107 450SLC
88 W124 300E
82 W123 280TE