The MB part number I have for citric acid is 000 989 10 25. You can get citric acid at a nursery or garden supply place. I don't know if it's clean enough to use as a cooling system flush.

The 83 SD had a coolant leak that turned out to be a cracked reservoir. I didn't associate the persistent puddle behind the right headlight with a leak. I thought it was spillage from filling the reservoir.

Sixto
95 S420
87 300SDL
83 300SD ... $950, see cars forum