Disco 1 rotary coupler issues (disco1 98)

Hi there,
A few weeks ago my front steering u-joint broke (i.e. was completely free and could not be tightened) in the middle of nowhere. Luckily there was phone reception and I was advised by my mechanic to remove and put it back it with the back side facing front. That worked really well and I was able to drive it back to a road and then back home.
A few days later I had the aluminum U-joint replaced by a steel one.
Anyway coming to the point...
Probably as a result of the steering wheel turning freely, the rotary coupler was not returned to its correct position and the next time I drove it off-road it snapped (I felt it when it happened). I have no horn and the SRS light is on (the cruise control was disconnected anyway).
I have a few questions regarding this part:

1) Is YRC 100350 the correct part number? (for a 98 disco1 with air bag and CC)
2) If I buy a pre-owned one (new is very expensive) how can I tell if it was removed in the correct position? I read somewhere that they should be taped when removed, but on ebay pics none seem to be taped.
3) How tricky are they to replace DIY?

Thank you for your input!

Ady

its the right number, buy one that from a firm that guarantees its good, not a bad job to do ,the screws holding on the air bag are perhaps the trickiest part

Thank you @jamesmartin . I ordered the part. Will give it a try.