Recover Overpayment from Ex

What is the name of your state? California

My 1998 divorce agreement states each of us will pay equally the back taxes owed (state and fed) for 1996 and 1997 through a joint bankruptcy. Shortly after the divorce, the bktcy was discharged.
I have now paid to the state and the IRS over half of the total amount due to date, my ex has continually delayed his payments.
Can I get a judgement against him for any amounts I now pay to the IRS in excess of 'my half'? I want to get these taxes paid because the interest and penalties are outrageous, but I don't want to get stuck paying the whole thing myself. (the total still due is over $8k) I filed a OIC with IRS to have the total split, it was denied.
Is this a small claims case?
Thanks.

My response:

You need to take him back to Family court, and file an "Order to Show Cause Re: Contempt". However, until you've paid all the taxes, you haven't been damaged and, because you never said the amount owed by him, I have no idea whether the amount would be within the jurisdiction of the Small Claims court.

IAAL