Hi Stevie,
It is indeed, but that lot then slide into another tube. And guess what, I've found the number, it's FTC1384!
I had a hunch and went to Stratstone in Perth. Had a look on there exploded diagrams, but no sleeve could be seen on the RRC pics.
However, I reckoned that new Defenders with ABS still use this bit. So, after looking at a new one outside we found the part on the Defender Rear Axle parts list. Just to confuse the issue, both the 1374 & 1384 are listed as sensor bushes, but the 1384 is an axle part and the 1374 is an ABS part.
Phew!
Only problem, they're listed at over £19 each!