The Truk rad started steaming last week
I removed the rad, plugged the pipes and filled it with water.
Once I'd carefully scraped the fins away from the wet bit I spotted the leak easily.
I cleaned it with wire wool & plumbers flux, then I tried using a gas soldering iron without the bit (like a mini blowtorch) but couldn't get enough heat into it. Next I tried my hot air gun and this did the trick! I was able to drop blobs of solder onto the hole and control the heat easily til I got a good dollop covering the pinhole.
I've only driven a few miles but seems to be holding

No-one will believe you...