Having come from an 8320 which served me well, I am now the happy owner of an 8900. I do have a question about the trackball. One my 8320 I am on maybe trackball #3 or #4. They were easy to change and if they started messing up I would pop a new one in. One the 8900 they can't be changed without disassembling the unit and most importantly, voiding my warranty. What experiences are people having with their trackballs. Are they quick to gum up or do they stay cleaner than the older 8300 trackballs?