Is there anything I can use to stop a leak at a threaded nipple pipe? Its on the mainfold of my boiler, and of course, it's the most inner pipe on the return line of a multi-zone manifold. I don't want to disassemble the whole manifold if I don't have to.

The pipe is about 6" long on the horizontal before it goes into a shutoff valve into the boiler and a T to the zones on the other side. Its leaking at the shutoff valve. I've tried to tighten it at the leak, but that makes the other end leak.

I might have just what you're looking for. Click on; PlumbingSupply.com - Leak Repair Kit (http://www.plumbingsupply.com/repairkit.html)
To check it out. There are others on the market if that don't fill the bill. Good luck, Tom