I have managed to make a similar repair in the past, by drilling the broken nipple stub and the stub still on the radiator out far enough to slip in a short run of copper tubing. I JB welded the copper tubing in the holes, and joined the nipples over the copper tube. Then I put the hose back on. Worked fine for quite a while, but, like someone noted the plastic is probably rotten from using Prestone green antifreeze. The main connection at the top of the radiator broke off, which I tried to fix the same way. That didn't last more than a year, so the radiator was changed out.

The failing plastic is not a good sign, but I would be inclined to fix the nipple first. Jim

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Own:
1986 Euro 190E 2.3-16 (291,000 miles),
1998 E300D TurboDiesel, 231,000 miles -purchased with 45,000,
1988 300E 5-speed 252,000 miles,
1983 240D 4-speed, purchased w/136,000, now with 222,000 miles.
2009 ML320CDI Bluetec, 89,000 miles

Owned:
1971 220D (250,000 miles plus, sold to father-in-law),
1975 240D (245,000 miles - died of body rot),
1991 350SD (176,560 miles, weakest Benz I have owned),
1999 C230 Sport (45,400 miles),
1982 240D (321,000 miles, put to sleep)