A seal for long-time exposures in oil and gas well tools. The seal is adapted for use in a sealed joint between two relatively movable members. In particular, the seal is designed for relatively slidable members. The seal has a body portion with a pair of annular arms extending from opposite sides thereof. A lip on each of the arms is adapted for engaging one of the relatively movable members. An elastomeric sealing element may be disposed in a groove in the body portion for dynamic sealing between the first and second members. Pusher rings may be disposed on opposite sides of the seal so that the seal may be clamped against one of the relatively movable members without the lips or arms longitudinally engaging either of the relatively movable members or a lock ring used to clamp the seal in place.