I'm not sure how long the the bold has a warranty, but if it is not under warranty and you feel comfortable, you could also change the trackball.
Cellular Nationwide Network - 3G, Sony, Panasonic, LG, SonyEricsson, Nokia, Tools, BlackBerry, has a bunch of trackballs and there are videos on youtube which show up how to assemble and disassemble the bold. Only do this if the above poster's method did not work.