Some of the milder stop leaks work fine. I have used that Prestone super sealer several times with no extra clogging of the heater core or anything else. It works pretty good to stop most leaks. I will warn you what it will do is make a mess all over your engine compartment if it leaks out some before stopping the main leak. Instead of ending up with sticky anti-freeze residue all over everything where it blows back, you will end up with this white looking stuff all over. It's easily washed off so don't panic. If your leak is bad you will get some of it on things till it stops it.
Also, after you get home and drain the system to fix it correctly, you will see a blob of jello looking stuff come out when you drain the fluid after using the prestone. Still, I never had any ill affects and once I flushed the system out everything was back to normal.
I was desparate one time and used that bars stuff for head gaskets, it looks like thick goo with copper flakes in it. This stuff will stop up various things, I would not use it unless I was in a real pinch. It even stops up the ports in the radiator cap for the overflow bottle. I have no doubt it would probably temp fix a head gasket, but with collateral plugging also.
If you do not have any hard pulls with your truck what can help is running the radiator cap loose so the system will not build pressure. The only reason they run the system under pressure is to raise the boiling point of the coolant. If you stay on the cooler side, around 200 F running the system without any pressure will help any leaks you have. You could also go to the store and buy a 7lb cap instead of the original 13 lb cap. This will be half the pressure, and still give you plenty of room for some hard pulls with the engine. I ran a 7 lb cap on mine for several years till I could afford a new radiator.
