Can anyone give any advice?

My husband & his ex wife have been divorced since 2003 and she got the car that was in his name and she was co-borrower but the judge did not make her refinance well 2 years after she gets a new car and not thinking about it I was looking at his credit report and it was on there when she made the payments on time but she called them to repo it so now it shows as a bad debt to him and was like $8000 I have contacted the credit bureus and disputed it but they said that they can't because he was first on the loan can I sue her for that amount to pay off the debt and maybe even sue her for more than that.Please if anyone can help me out before I have to pay a lawyer for a consultation.