I’ve routinely used silver to braze these on, and haven’t ever had an issue. My preferred technique, which does take some practice to get stuff aligned nicely, is to heat up the spot on the tubing; melt on a small dollop of silver; hold the pump peg with needlenose around its neck, heat it up (well fluxed of course) until it’s at the brazing temperature then hold it onto the tubing while remelting the silver around and under it. I don’t look to get a fancy fillet around it. Best to practice a number of times on scrap until you get the hang of it. Or fabricate some kind of jig to hold it in place and braze as per usual, but I’ve not bothered with this.