I just looked in my 603 shop manual. The 603 does not have any short connecting hoses like the 617 so it looks like the water pump itself is the source of your leak. If no one has a better suggestion, I would recommend replacing it. I've never done that job but it doesn't look difficult, just a lot of stuff to get out of the way and maybe buying some large Allen wrenches if you don't already have them.

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"Buster" in the '95

Our all-Diesel family
1996 E300D (W210) . .338,000 miles Wife's car
2005 E320 CDI . . 113,000 miles My car
Santa Rosa population 176,762 (2022)
Total. . . . . . . . . . . . 627,762
"Oh lord won't you buy me a Mercedes Benz."
-- Janis Joplin, October 1, 1970