A seal for sealing a rotor of a rotary machine to a stator thereof which circumscribes the rotor and is separated therefrom by a gap comprises a nonrotational sealing element received within an annular slot in the stator and radially translatable with respect thereto, and extending into the gap for sealing to rotational sealing element carried by the rotor. A resilient biasing element received between the nonrotational sealing element and a floor of the slot biases the nonrotational sealing element radially inwardly toward the rotational sealing element and limits radially outward movement of the nonrotational sealing element. A guide extending into said gap from the slot engages the nonrotational sealing element to prevent axial misalignment thereof with the machine's rotor.