The University of Cape Town source is easily the most valuable
but we still have no real info on cause.
Sounds like a navigation error,
but it could have been a machinery failure, or ...
At this point leaving cause blank.
Sources split between 15,000t and 4,000t for spill volume.
CTX went with 4,000 because Underhill is easily the most detailed source,
and, being concerned about penguins, unlikely to under-estimate spillage.
This volume seems to be accepted by most of the South African sources.