They are easy to replace......and not.
I've used a bunch of TRW's and they're pretty good. Of course, an original German one should last for 40 years!
Swapping the box is pretty easy. Making wicked sure that the steering wheel AND the front wheels don't move AT ALL during the swap is the hard part, otherwise you'll be after a new front end alignment, for sure.
The box is attached to the torsion tube with clamps, but there is a notch on the side of the box where it mates with the torsion tube, and a corresponding tooth on the torsion tube. The tooth fits into the notch for steering column alignment. No big deal there.
So......The process is, after setting it "straight", securely anchor the steering wheel from movement. Make sure the front wheels are on ramps or something so they won't move. Remove the Pitman Arm from the steering box shaft (this needs a 1/2" drive bat handle and a 4' piece of pipe on it). Leave the tie rods attached to the pitman arm. With the pitman arm loose but still on the splines, re-check that the steering wheel is straight. Remove the steering coupler bolts (I usually remove the entire coupler disk to make it a bit easier), remove the pitman arm from the box, loosen the clamps for the box and remove it.
I can't remember if VW boxes have a keyed shaft to the pitman arm or not. If it's keyed, that makes the installation process easier (it can only go on one way).
Installation is the opposite, but before installing the box, do the best you can to turn the steering wheel shaft on the new box completely from lock to lock, then determine the approximate center of the sweep. Swap the steering coupler end from the old to the new box - it only goes on one way, but don't fully tighten it yet, you'll need it loose as you adjust things.
Install the box. Line up the upper and lower steering coupler flanges as best you can, not moving the steering wheel, then install the coupler to the steering wheel shaft side only (2 bolts). It is sometimes handy to loosely install the box flange bolts, just to keep things kind-of lined up.
Install the pitman arm. You will probably have to jiggle the box input shaft a skosh to get the splines to line up. It doesn't take much movement of the box input shaft to pick up the splines and you can turn it with a pair of vise grips on the shaft. Once everything seats, re-align the box input shaft "T" fitting by turning it on the shaft to align it. If it's really off, then remove the pitman arm and fiddle with the box input shaft to get things better lined up, then re-attach everything.
You don't have to have the steering box perfectly centered in its sweep - close to center is good enough. What you're really trying to do is avoid a new front end alignment. Once the pitman arm nut is torqued to spec, take a chisel and peen two places on the nut collar into the slots on the shaft to lock it in.
If you get it all done and the steering wheel is a little off when driving straight, then you can pop the steering wheel off and move it one spline or so to bring it back to center.
Use a VW service manual for tightening torques.
