After riding a WR426 for 4 1/2 years without any problems (15000 miles), I purchased a 2006 YZ450 hoping it would be half as reliable as my 426. It hasn't been, a fork seal went at 40 hours, water pump seals went at 115 hours, and now I have a cracked swing arm. Make no mistake this bike is maintained perfectly, (much better than my 426) all bearing disassembled and greased, oil changed every 3 hours, cam chain changed at 100 hours, valves checked/adjusted, fork oil changed twice, coolant flushed and replaced etc. The cracked swing arm is a big deal not only because the cost of a replacement but more importantly had I not looked really closely at the inside weld and noticed the crack it quite possibly could have resulted in a failure on landing a big jump. I'm 44 years old, 193 pounds I ride fast but I'm not crazy. This bike has only been down 4 times all low speed (wet track slide falls) no damage at all. I had my local dealer look at the swing arm and they have no idea what I could have possibly done to cause this. They sent pictures to Yamaha and their response was tough it's passed the 30 day warranty. I can't be the only one with this problem, check your swing arm. It looks like Yamaha's quality has suffered since 2002 this will probably be my last Yamaha and that's to bad because Yamaha is the only brand I have owned.