I assume the rad is the "old fashioned" copper/brass type. A pinhole in the brass tank/tube can easily be repaired by anyone who has soldering kit. A DIY job even with a soldering iron for a pinhole. Just make sure the metal is thoroughly clean and use solder that has built in flux. In the rad factory I worked in we had a test/repair section just before the paint booth where such repairs (and bigger ones) were done. They used a blowtorch/painted on flux/solder. The worst repairs to do were to the seamed tubes in the core block due to lack of access and more leaks popping up due to excess heat.
Thanks - if K-Seal doesn't work I might give that a go.
Mark
