I did an XD one for a friend about 18 mths ago - similar story.
I replaced the O ring on the bottom case that seals the pitman arm. Ordered in the suppossed actual replacement - didn't look like it would seal my pinky.

It is a pretty dodgy setup, and I wasn't totally happy with it, as any slight leak, the box drains, and you have bugger all steering.

I suppose you might need to go back to a manual steering box.

The quickest way to replace the box, is to drop the pitman arm off, take out the brake booster, and pull it out that way, done it before.
You can get seal kits for them, BUT, you need some special tools to fit some seals. An example is the worm shaft seal, it goes in from the inside.
Another thing to consider is, how good are the needle bearings for the sector shaft?? and how are the bearing surfaces on the sector shaft??