Chainsaws

Blown Seal on Crankshaft...I have owned a Husqvarna Model 359C that was purchased at a big box store in 2003. I have loyally fed it the proper oil/fuel mixture, used a good grade of chain oil and always verified that it ran freely, cleaned the air filter each use, kept the blades sharp, kept the motor free of sawdust, and stored it indoors. I use it around the house no more then a few trees a year. Last week it quickly overheated, stalled and would not start. It had spark and would turn over easily but had low compression. The shop I took it to said the "seal on the crankshaft failed." He said the rings were not broken. He said it had been "starved for air." I guess I don't understand if the filter was clean and the proper oil/fuel was used, why did this happen? What did I do wrong? Did I just wear it out or is this problem common with this model? I really liked your product/my saw. It has served me well. I plan on buying another.