Radiator repair

[Radek]

Hello all;

The radiator in my 1988 909Q (OEM Behr, plastic ends, aluminum core) started to leak at the top, where the joint between plastic and aluminum is.  Has anyone successfully repaired this kind of radiator (JB Weld, glue, solder)?  
Freezing temperatures outside make a quick fix preferable.  Perhaps one of those stop-leak bottles would work?
Thanks.

Radek.
88 90Q
91 V8Q 5-sp