A bearing isolator seal for installation within a machine assembly including a housing having a generally annular bore, and a rotatable shaft disposed concentrically within the bore, the seal comprising: a generally annular stator having an outer diameter face receivable coaxially in the bore and an inner diameter face mountable coaxially on the shaft, and the stator extending longitudinally between a first end face disposable in the bore and a second end face having a generally annular first groove formed therein, a generally annular rotor rotatable with the shaft, the rotor having an inner diameter face mountable coaxially on the shaft and an outer diameter face, and the rotor extending longitudinally between a first end face disposed opposite and axially spaced-apart from the second end face of the stator and a second end face, the rotor first end face having a generally annular second groove formed therein, and a generally annular diffuser ring disposed between the stator and the rotor, the diffuser ring extending longitudinally between a first end portion mounted within the stator first groove and a second end portion received within the rotor second groove, in which the rotor groove has an end wall disposed facing the stator second end face, and the diffuser ring has an axial length extending longitudinally between the first and second end portions, the length being selected such that diffuser ring second end portion is abuttable against the rotor groove end wall to maintain a predetermined clearance between the stator second end face and the rotor first end face characterised in that the second end portion of the diffuser ring is received within the rotor second groove in a substantially non-contacting relationship therewith, the diffuser ring second end portion being configured as a radially outwardly-extending flange portion and the diffuser ring having a circumferential recess formed in it between the first and second end portions so that it has a generally-C-shaped axial cross-sectional profile. a generally annular stator having an outer diameter face receivable coaxially in the bore and an inner diameter face mountable coaxially on the shaft, and the stator extending longitudinally between a first end face disposable in the bore and a second end face having a generally annular first groove formed therein, a generally annular rotor rotatable with the shaft, the rotor having an inner diameter face mountable coaxially on the shaft and an outer diameter face, and the rotor extending longitudinally between a first end face disposed opposite and axially spaced-apart from the second end face of the stator and a second end face, the rotor first end face having a generally annular second groove formed therein, and a generally annular diffuser ring disposed between the stator and the rotor, the diffuser ring extending longitudinally between a first end portion mounted within the stator first groove and a second end portion received within the rotor second groove, in which the rotor groove has an end wall disposed facing the stator second end face, and the diffuser ring has an axial length extending longitudinally between the first and second end portions, the length being selected such that diffuser ring second end portion is abuttable against the rotor groove end wall to maintain a predetermined clearance between the stator second end face and the rotor first end face characterised in that the second end portion of the diffuser ring is received within the rotor second groove in a substantially non-contacting relationship therewith, the diffuser ring second end portion being configured as a radially outwardly-extending flange portion and the diffuser ring having a circumferential recess formed in it between the first and second end portions so that it has a generally-C-shaped axial cross-sectional profile.