I had the same problem, but at $200+ for a toyota one, there was no way it was being replaced. However the mast was only $60 (still not that cheap) When you pull them appart, there is a little cylindrical piece of metal that keeps the nylon "rack" in contact with the drive gear. The metal piece had a flaw in it that didn't keep the rack directly in contact with the drive gear, thus destroying the rack. Obviously, this kind of fault is relatively common, so have a look at the piece of metal pushing the rack onto the drive gear. All I did was buy the new mast and turn the metal so that the flaw faced away from the rack (superglued in place so that a repeat could not occur) and haven't had any trouble since.
My car is a daily driver and I haven't had any trouble in 4 years since.