Upon opening up my recently purchased 745 with a B234F engine, I found a stripped balance shaft belt and one seized shaft. I wonder if this is common and what might be the cause? I expect to have to remove the balance shaft assemblies and replace the bearings seals and O rings, but I want make sure it will not reoccur. Also the tools shown in Volvo's book look expensive. I am hoping for some background on this problem. Wayne