This information is unconfirmed but the source is highly reputable:
We just received word this morning that the Transocean Marianas rig has developed a large crack in one of the pontoons on the #5/#6 anchor chain locker while they were picking up anchors, and is currently taking on water and listing. The bilge pumps are keeping up (barely), but there’s certainly concern that it might sink on location. So far, 68 people have been evacuated from location.
According to RigZone, the Marianas was working offshore Nigeria. [Per one of our readers, (see comment below) Petrodata shows the rig operating offshore Ghana.]
More: The Marianas, spudded the Macondo in October, 2009, but was damaged by Hurricane Ida and towed to shore. The Deepwater Horizon was the rig that replaced the Marianas.
Bud's Offshore Energy (BOE) 