I have, in the past, had some success with a teaspoon of medium grind pepper. I have NOT done this to any of my Benz's.
(I think it was 2 Ford F250's, that I tried it on, and it worked on a couple of pinhole leaks)
Buy the new radiator. I may need a new one in my 420SEL soon too... I might just try some pepper just for grins, to see if it works. Note: whatever is used to stop the leak, is only a temporary fix.
"...rationality of thought imposes a limit on a person's concept of his relation to the cosmos." -Nash
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09 Jetta TDI