Steering Gear Box Sector Shaft problems of the 2001 Chevrolet Tahoe

I have a 2001 chevy Tahoe & a 2003 GMC sierra. Both vehicles make a clunking noise with lots and lots of vibration in the front end when turning corners or moving slowly over bumpy areas. I was told that the steering shafts are bad. The GMC has already had the steering shaft replaced and the problem is back. The Tahoe I purchased used and the previous owner told me about the problem and said he has taken it in for service and they pack the steering shaft with grease. My father in law has a chevy truck and is having the same problem. I don't understand with such a huge problem on a variety of years that this is not recalled. If you can check into this problem and if there is any solution other than continually re-greasing the steering shaft which is a very expensive and time consuming job. Talking with others with the same problem, I have heard that the steering shaft will eventually wear out and I don't know if this could be dangerous as far as causing an accident if something happened while driving. I have two young children that I drive around constantly and I am somewhat worried about this problem. Thank you for your time and consideration in this matter.

I have a recurring knocking in my chevy Tahoe 2001 steering column that has to be serviced every 8-10 mos. I would like to know if this is something that has been investigated as a problem/concern of other consumers. The dealership states that the knocking is caused by some type of calcium build up around the steering column at a cost of $200-300 each time this problem is repaired. This has been occurring since I purchased the vehicle in 2001. I do not feel that this is something that I should be continually paying for annually. This is not a rare occurrence. Is there something that can be done on gmac's end to repair this problem without any monetary loss of the consumer?.