Oh Lori, I'm so sorry to hear Disney is starting to show her age.

As for the smell in the ducts, it's possible that some of the urine seeped down into spots you can't get to. Maybe try just pouring some of the disinfectants/deodorants down the duct and hopefully they'll seep into the same spot the urine did. The only other thing I can think of is to call one of those duct cleaning places. They'll probably want to come and clean all the ducts, but maybe they'll be nice enough to give you some hints over the phone.