Is the end tank plastic? There are Fiberglas/epoxy repair kits available at auto parts stores for about $20. I don't know for sure whether they would work on a radiator but it sounds like you've nothing to lose. I have successfully used a kit like this to repair a leaking monovalve.

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"Buster" in the '95

Our all-Diesel family
1996 E300D (W210) . .343,000 miles Wife's car
2005 E320 CDI . . 148,000 miles My car
Santa Rosa population 177,300 (2026 projected)
Total. . . . . . . . . . . . 668,300
"Oh lord won't you buy me a Mercedes Benz."
-- Janis Joplin, October 1, 1970