Update at https://blogs.nasa.gov/spacestation/2023/10/09/international-space-station-operations-update/
Roscosmos confirmed that the observed leak is on Nauka’s backup radiator, which is mounted to the outside of the module. The radiator was delivered to the space station on the Rassvet module during space shuttle mission STS-132 in 2010. It was transferred to the Nauka during a Roscosmos spacewalk in April. The primary radiator on Nauka is working normally, providing full cooling to the module with no impacts to the crew or to space station operations.
Teams on the ground will continue to investigate the cause of the leak, and additional updates will be made as available.