I have a TX-472MDP which I put up this spring. I purchased it used
and it was about 2 years old. I had the same problem. There was a
spot about 2/3 up at which the tower would stick and bind. I tried a
new belt, but that didn't help. You may notice that you can tighten
the belt by lowering the motor drive. This didn't help either.
My tower had some kind of lubrication on the legs that was like a
thick grease that had gotten very sticky. I called US Tower and was
told that there was a time when they used this stuff to lubricate the
legs for nesting during assembly. I was told to use paint thinner or
lacquer thinner and clean this stuff all off, since it's not needed
once the tower is assembled. I laid the tower over and carefully
cleaned this stuff off. It took about 3 hours. There was a
particularly rough spot on one of the legs that I then painted with
"Slip-Plate", which is a paint that has graphite in it.
Since taking these steps, the tower has worked flawlessly.