A seal segment has an arcuate body having: a first end; a second end circumferentially opposite the first end; a first face; a second face axially opposite the first face; an inner diameter (ID) face; and an outer diameter (OD) face. The seal segment is shaped to interfit with a plurality of identical seal segments first end to second end to form a seal surrounding a central longitudinal axis. The first face has: a circumferential channel closer to the ID face than the OD face; and a plurality of channels extending from the circumferential channel to the OD face. The ID face has: a circumferential channel closer to the first face than the second face; and a plurality of channels extending from the circumferential channel to the second face. The ID face circumferential channel has an open end.