Does anyone know of an easy fix for this.
Call a plumber.
Is that a Okum-Lead joint?
It almost looks like the cast is rotted at the joint, but if not you could reseal the joint with okum & lead if you know how…I have done it many times YEARS ago—
Probably the easiest would be cut that portion out and use two calder couplings after a new ABS cleanout is installed with ABS stubbed from each end of the cleanout.
Pound in the oakum rope, pound in the lead.
Gotta be faster to beat Dale nowadays !!
okum and plastic lead will work or snapping the cast and intalling PVC with fernco adapters.