The best trans gears I ever found were from original HD knuckles, old and shiny or otherwise. I have zero scientific basis for saying this but I strongly suspect that heat treatment way back when was the key to making them last forever. My experience is that they do if you treat your trans right and change the oil often. The strongest cases I ever found were early 1970s Supergilde. Remove the four studs, change the guts (or just the mainshaft), and they work just fine with your jockey lid.
New Knuckleheads? Thank, you, Jesus!!