Encapsulation may be the way to go, but the tape is pretty nasty. Moldy, fraying. I'd rather have it removed but still considering encapsulation.
Based on what I've found online, removal of tape on ductwork shouldn't be overly expensive. If we are talking $1-2K I may bite the bullet simply to allay my neurotic fears.
Thanks for the opinions, guys. And I did think about the reporting/disclosure issues Piob. Good point.