I've just re-built the steering box on the LC. In order to practice first, I bought an Omega steering box from eBay and stripped it down. Think it was about £30, and it came with the steering arm and centre link still attached. I was hoping that some of the parts, perhaps even the complete steering box would fit the LC, but unfortunatley everything is just a little bit different.
Assuming it's not just the PAS fluid input/output pipe junctions that need tightening up, to leak to the outside world there are only really a few places it can do so.
1) Bottom of the steering box - where the steering arm is. There is a lip seal on the output shaft here.
2) Top of the steering box, under the alloy plate with 4 bolts and the tension adjuster. There is an O ring under here.
3) Junction of the PAS pressure box and the main body - another O ring here.
4) Under the PAS pressure modulator Servotronic solenoid. Couple of small O rings here.
5) Steering column input shaft. Lip seal here.
You can probably replace any/all the the O rings in 1 and 4 without a complete strip down - perhaps even with it still in the car. However the two lip seals will need pressing out, and to get that far you really might as well replace everything
So it all depends exactly where it is leaking from. A complete seal kit is available (from Bulgaria!) on eBay for about £70. That doesn't include the 3 bearings - two of which will need to remove - they will be another £100 or so.
In short - I'd probably throw another second hand PAS box at it. Will be cheaper and less agro. Try to get one from exactly the same spec Omega - there are lots of subtle changes, and even different length of steering arm. You can swap the arms from one box to another, but they're on effing tight and you will need a decent puller, and probably some heat to persuade it to come off.