I have used an IR thermometer and aimed it at cold exhaust flanges, when it got to the leak it popped up to like 300 - 400 degrees. Here's a pix.

 

This stuff works GREAT!!!
I used it on my wifes car, her radiator was leaking at the seam on the passenger side, shook it for 1 min, poured it into the cold radiator, and drove for 30 min, parked the car and let it sit all night, has not leaked for over a month now.

Amazon.com: K-Seal ST5501 Multi Purpose One Step Permanent Coolant Leak Repair: Automotive

I would try it, the only way it will clog the radiator is if you use to much, only use one bottle, if that does not work then you need to bite the bullet and fix it right, it should be fixed right in the first place, but this would get you buy.

 

K-Seal is currently in my 03 Disco and it made a tremendous improvement so far! ( 3 days ) but since it has quietened down the truck I can now hear other little things ! my idler pulley, a/C condenser fan humming, a little wa wa wa hum coming from rear tires or drivetrain seems more towards rear and only at 40mph ... I'm dont really know how "smooth" these are supposed to sound either... but doesn't seem like it will blow up! lol