My radiator had a pinhole leak from one of the plastic side tanks.
It was leaking from the seam that runs on top of the tank, near the upper hose on the driver's side. Didn't notice it until I was under the jeep doing some inspection of underside damage from some unforgiving rocks, when I saw the trail of evaporated coolant running down the side of the tank.
Ordered a new radiator online, since the local dealers wouldn't match the online price.
I got two bolts shy from removing the radiator for replacement, when I was blocked from success by the previous owner's installation of an RV tow bar, which prevented access to the lower two bolts that hold the radiator to the condenser.
Removing the tow bar seemed like a supremely unpleasant task, without any idea of what kind of special contortions I'd need to use in order to either remove the tow bar or loosen it enough to gain clearance to remove/replace the bolts holding the radiator in.
I admitted defeat to the tow bar, and re-installed all the bolts, hoses, fan shroud, fan, from grille, etc.
Pinhole leak should be easy enough to fix right?
Well, from previous experience in the field, I found that RTV does not seal (used the high-temp orange stuff... all that I had with me at the time). Neither does JB Weld (although the JB Weld slowed the leak enough to allow me to drive 2 hours at highway speeds to reach the nearest shop that could replace a radiator).
This time, instead of being in the desert, hours from the nearest parts store, I had all the sealers, glues, epoxies, etc in my house and garage.
I started with 5 minute plastic epoxy (loctite). Let it cure for 48 hours. It leaked.
Next I tried JB Weld Plastic epoxy. I removed the loctite plastic epoxy, which scraped off pretty easily. I've had good results with the JB Weld Plastic; my rear hatch handle snapped off in -20F, the plastic weld has fixed the hatch plastic for over a year, although it looks very ugly (plastic weld's grey color doesn't match the black laredo trim very well).
So I got a wood chisel out, smoothed out the seam area that had the leak, and mixed up some of the JB weld. Applied it to the plastic tank, waited 48 hours for a good cure, and Bingo! No leaks!
So if you're in a bind (offroading and hitting something hard enough to do some damage to the plastic bits on your radiator), it might behoove you to preemptively put a tube of JB Weld Plastic epoxy in your Jeep!