hammer6605-17-2011, 03:07 AMi have had good luck with npk breaking mostley ledge and granite boulders .we bought ours new for about $100,000 onley changed the tool twice since 2005 the host is a 330 cat excavator. it is critical to grease the tool often,you can replace the tool bushing,check the bolts on the rubber mounts for breakage hope this helps a little.