Hi - thanks for requesting me. I'll be glad to assist you.
Here's the Oklahoma statute that applies:
R.L.1910, § 6644.
§6070. Boundaries and fences.
Coterminous owners are mutually bound equally to maintain:
1. The boundaries and monuments between them.
2. The fences between them, unless one of them chooses to let his land lie open as a public common, in which case, if he afterwords encloses it, he must refund to the other a just proportion of the value, at that time, of any division fence made by the latter. R.L. 1910 Sec. 6645.
Thus, according to this statute, your neighbor
would owe 1/2 of the cost of repair of this fence. If the neighbor refuses to do this, then you would have the right to sue and seek to recover 1/2 of your cost.
Thanks for allowing me to assist you, and if you have any additional questions, please don't hesitate to ask.