So, I have a number of nipples rounding that I want to replace. I got the new nipples and went to replace the old ones, but I found that when I try and unscrew any of the old nipples, the flat head screwdriver is stipping the screw head of the old nipples. I've tried like four or five different flat head screwdrivers and they all tear apart the screw heads. Is there a better tool for this or different technique? These nipples are probably pretty old, like maybe 10-20 years old.
Try soaking the threads in Liquid Wrench. Are the spokes worth saving? You could cut them out and replace with new spokes and nipples. Be sure Your spoke wrench fits the nipples tightly before installing the new nips.