In article , Robin Graham
writes
If you place the top on top of damp cactus compost, it
should root and within a few years get back to 18 inches; meanwhile, the
stump will send up one or more offshoots from the top.

Yes, I agree. Unfortunately the stump is most of the plant, i.e. about 12"
and it would be a pity if it had a truncated top, albeit with shoots growing
from it. It's taken many years to get this far!

What on earth was eating it?

Don't know. Part of the stem was going brown and shrinking and I could see
that if I didn't do anything the bit above this would die off completely.

Sounds more like rot than being eaten.

--
Kay
"Do not insult the crocodile until you have crossed the river"