How hard is a power steering gearbox rebuild? 73 dart

The power steering gearbox on my 73 Dart leaks bad and I have to do something. It leaks where the steering column goes in and the pitman shaft comes out. A mechanic told me the bearings inside are worn and that allows the shafts to move sideways and ruin the seals.

Is replacing the bearings and seals something I can do or does the unit need to be sent away for a rebuild? I'm looking for options. I would prefer to repair the original or have it done. Does it require special tools? Where can I get the parts? Where can I send it out to be rebuilt?

Thanks, Tom