Pepper is an old, old, remedy for leaking cooling systems, and yes it will work temporarily. I have used it to stop a heater core leak and it lasted for about 2 weeks in a daily driver, at least it got me by until I could get to the job, and change it.
If you want to stop the leak without plugging the cooling system, Bars Leaks has probably the best selection of anti leak choices for cooling systems. They make the pellets that GM sells, and more options, depending upon what problem you have with your system.
I've seen cracked combustion chamber cutaway cylinder heads that had over 50,000 miles since the treatment, that functioned until the car was scrapped. It was sealed, and done, never a problem after the treatment. This was the pelletized formula. I have used the pelletized formula in my own cars and customer cars and it has worked flawlessly for external leaks as well as head gaskets, unless the head gasket was just too bad to effect a seal, and repair.
Having worked in many different GM dealerships, as Mike alluded to, GM puts the pellets in all their cars to minimize warranty repairs for minor leaks, exactly what you're chasing with your own situation currently. Either the pellets, or the pelletized formula will most definitely work to seal a minor leak that you're experiencing.
Myself, I'd never go through all the work involved to hunt out a minor leak and do all the labor to think you have it fixed, only to find you have a porous casting, and didn't fix it by mechanical means anyway. Working at GM dealerships I've seen a few new porous castings. When GM sold the car new, it had pellets in the cooling system, using them at this point is doing the same thing GM does to effect a permanent repair without any cooling system detrimental problems.
If it were my car, I'd but a Bars Leaks product in it, and forget it...............
When I had my own garage I was friends with a guy that owned his own raditor shop, when they did a radiator repair the tossed a couple spoonfuls of flax seed into the radiator before they returned it to the customer. This did the same thing any of the stop leak products did by giving a little extra insurance to minimize comebacks, for what it cost to put a little flax seed in there it was real cheap insurance. Radiator shops buy the flax seed in containers, just for this insurance aspect.