One thing that can cause occasional guru's, are viri...
They are so rare in the Amiga world now, that most people don't bother thinking about them at all. If you have tested lots of old disks on your A2000, chances are one or several of them were infected and you transferred the virus to your hdd. As most viri are rather out-of-date, most don't work at all or they cause major lock-ups, such as guru's.
Try a decent virus-scanner to check this out before you start resoldering all your IC's :-)
