Besides financial contribution, what crucial, near-irreplaceable operational capability does Russia historically provide?

Answer

Propulsion and control for orbital reboost maneuvers

Russia’s contribution in keeping the station up is functionally irreplaceable because the ROS contains the Data Management System that handles Guidance, Navigation, and Control (GNC), and Russian spacecraft traditionally handle orbital reboost maneuvers.

Besides financial contribution, what crucial, near-irreplaceable operational capability does Russia historically provide?
SpaceISSspace explorationInternational Cooperation