If you have an original 25D type distributor this is an upgraded arm (blade moulded and riveted )for performance use because all the other types available now are likely to fail at high revs. Because the blade is thin,or the rivet sometimes to long and not moulded correctly it becomes loose at the rivet and shudders or current can arch down to the distributor shaft causing electric engine failure. The material used on cheaper versions also contains more carbon blacking and is therefore more conductive.