I don't know where you are at on this, but my 2001 Ranger started to have an antifreeze smell in the heater. The local auto parts store and others highly recommended the stuff AlumaSeal in the little tube for a couple bucks. I had nothing to lose so dumped it in. The smell went away pretty much and well within the recommended 300 miles. I have driven over a thousand miles since and it is fine. If it lasts through this winter that is better than changing out the core which my shop said is about a 5 hour job. Who knows, what if I paid to have it changed out and then the truck got totaled. Why spend $500 or so if you can delay it for a year or maybe longer. The one thing though is don't put more in if the first tube doesn't fix it. That is where people get plugged radiators etc. Too much of a good thing can be bad. You have nothing to lose but two bucks to try it.
Well, I hope the guy got his heater core fixed with less bickering than was in this thread. Sure wish posters would post the end results/procedures/fixes so we could learn something and become more knowledgeable.