The puller is a great idea. Gotta make one. Are you really using a 6X32 tap? That would require a drill bit to be used before the tap, I've been using a taper 2X56 because it will thread right into the existing hole, might be why I'm breaking them. What is your method of getting the retainer out of the end so that you can replace the disc and still use the retainer again? All the ones I've pulled out have the rim flanged over the retainer and I'm sanding them down flush with the top of the retainer to avoid damaging it while prying it out.I must be lucky as all the brass inserts I have pulled so far had a fairly thick bottom end to them, the thread of the machine screw barely makes a mark in the brass but holds strong enough to pull it out of the carb body. I did use a bottoming tap once but found the machine screw to be better to hold and pull the brass valve body out with. I made up a puller that a long nut on the machine screw can thread down the shaft and it applies enough force to pull the brass part out with little effort. Think of a steel bar 1/4" X 1/2" X 1.5 " long with a hole in the middle, thread the screw through the hole and then into the brass nozzle body , the bar spans the carb body resting on the outer rim , then just run the nut down. When it contacts the bar a couple turns with a wrench or pliers and the valve body pops right out undamaged. I found using a new machine screw each time gets a better hold on the valve body, I have lots of them in the screw assortment tray.