Worn teeth on the steering shaft

Okay, my steering has been bugging me for a while. I replaced power steering pump and pulley it helped my steering because it was definitely bad. I had written in a previous question about a pull or a tug while I'm driving. Not all the time just once in awhile. The longer I drive it the worse it seems Today I had a friend turn the wheel while I looked under the hood with a flashlight. Lo and behold I saw something shiny. It is a worn tooth in the gears on the shaft The only reason I saw it while she was turning the wheel was because it was shiny compared to the rest of it. How hard is this part to replace and how long can I go before it's dangerous? Are there any quick fixes? I have a few projects going on right now with an entire exhaust being put on then body work and certainly did not need this. I know this is a common issue how hard is this job and what do I need I guess. Can that tooth or teeth be ground down or do I need a full replacement? I know a little about some things but. I have never had this problem before. Thanks.