I have a fairly recent 14" Delta bandsaw which has been pretty accurate through most of its life.  Until, out of the blue, is snapped the upper wheel mount.  Delta cheerfully replaced the part, but for some reason, the blade suddenly developed a tendency to yaw when resawing under full steam.  I decided that, if I was going to go through all the adjustment hassle I might as well extend the height as well.  To my surprise and delight, this worked, but the blade would intermittently wander, and then, just as suddenly start working perfectly again.  Definitely time to tear my hair out.