Go after seller for wrong disclosure?

[Le Trinh]

• Cedar Hills, Utah: We closed the house in late June 2019. The house has partial-finished basement. We engaged a builder to finish the basement mid July 2019.
• After the builder submitted the plan for the un-finished part, it took the builder and the city a while to find out that the previous owner finished 3 rooms (2 bedrooms and 1 living room) without permit. 
• As we found that out, the builder looked closer to the 3 rooms and advised us to remove all the existing drywall and ceiling. Without that, he has already known 2 issues with the 3 rooms: missing fire block, wrong insulation, wrong heat duct (they open it from the existing duct that is used for the first floor – to get heat in the basement, it is wrong, it needs to have a separate duct).
• And only after removing all the drywall and ceiling, our builder will be able to tell us if there is anything more to be fixed to bring it up to code.

We finally have the certificate of occupancy for the entire basement today - after 8 months. With the extra $ we spent and the stress we went through, is it worth it to go after the previous owner? for failing to disclose that there is part of the house completed without permit? With them being in the construction line, I don't believe that they are not aware. But they can claim that they did not know they need to pull a permit?