I'm not a dba, and have never tried 'cracking' a database.
AFAIK, You cannot retrieve an encoded DBA password, except by:
1. Asking the DBA what it is.
2. Running a 'cracking' program.
3. Dumping and Loading the database, and restoring an old user table to it.
Post your question on the DBA list with something like 'Lost DBA password' in the title, and you may get a better response, as DBA types may not be looking in this section.