Okla. Stat. tit. 16, § 16-23: Notice of suit to grantor

In all cases where an action is brought against a grantee to

recover real estate conveyed to him by warranty deed he must notify

the grantor, or person bound by the warranty, that such suit has

been brought, at least twenty (20) days before the day of trial,

which notice shall be in writing and shall request such grantor or

other person to defend against such action; and in case of failure

to give such notice there shall be no further liability upon such

warranty, except when it is clearly shown that it was impossible to

make service of such notice.