To address the problem of flush fluid leakage under normal operating conditions in rotary machinery, an improved pack-box has been conceived. The pack-box has a rotary bearing concentrically disposed within the pack-box, wherein a circumferential segment of the rotary bearing is circumferentially fixed within the pack-box. The pack-box further comprises a wall-step that defines at least a first thermal expansion channel and an inner wall that defines at least a second thermal expansion channel.