They can't be lubed and they do go bad but not that often. They are expensive ($100-150?) and I'm not sure if your local parts store carries it and I've never changed one so I can't comment on the difficulty (doesn't look that bad though). I don't think it will hurt anything to keep driving it for the time being...

'97 4Runner, '06 F350, '86 4Runner, '05 WR450
http://home.4x4wire.com/erik