Luckily, using the AS OF flashback clause I can rewind time and get the code back.
(NB: To get this to work I had to SSH to the server and connect as SYS via SqlPlus)
SELECT text
FROM sys.dba_source
AS OF TIMESTAMP TO_TIMESTAMP('2016-01-26 12:34:00', 'YYYY-MM-DD HH24:MI:SS')
WHERE owner = 'schema'
AND name = 'object name'
AND type = 'PACKAGE BODY'
ORDER BY line
;
Change as required and carry on.:-)