It has already ben mentioned, but if you haven't run Disk Utility > First Aid a
second time it is worth trying. DU has never been any great shakes at volume repair, but sometimes a second or even third pass will finally clear up an otherwise implacable error.
FWIW, my advice would be, if you are looking for an excuse to get a new MacBook, MacBook Air, MacBook Pro, this is the best excuse you are likely to get. If not the ~$100 cost of
Diskwarrior,
TechTool Pro, or
Drive Genius would cost is a
LOT cheaper than a new Mac but there is no guarantee that any one of those will fix the problem. Of those three DiskWarrior has arguably the best reputation for repairing volume errors, but TechTool Pro will run a surface scan and provides detailed S.M.A.R.T. data reports which are far and away the best means of identifying impending drive hardware failure.
