I agree with just giving it a day or two to stop... if you just hooked it up. That worked for me. If its been going for a while and then just started leaking, then you'll have to take apart and try to reseal.
The pencil trick was one I learned from a plumber who'd been retired longer than I was alive, and could still outwork me 2:1. That guy knew more tricks than McGuyver for sure.
Once we cut a copper line, and the valve right behind where we were working wasn't holding, so there was a slow trickle of water coming out. He took a slice of wonderbread from his sandwich and stuffed it in the pipe. It held long enough for us to sweat a new valve in-line.
That's why it's called wonder bread, I thought it was because after processing all the goodness out of the flour they then added them back in, making it healthy again!!!
