Still might be worth looking into.
After the downgrade, I used the automatic update, which had previously failed to work as an attempt to upgrade back to .11. Happily enough, it updated back to .11 and Automod was suddenly present and working again.
(The side effect of the previous install had the downgrade, and Automod not appearing in the ACP.)
Again, might still be worth looking into by someone with more time and skill than I.