A fluid separation centrifuge for the separation of particulate matter from a flow of oil is designed with a disposable rotor assembly including a molded plastic rotor housing and a fluid separation device positioned within the rotor housing. Included as part of the fluid separation device is a unitary, molded plastic base plate which is designed and arranged with a peripheral lip formed with a channel portion therein. In a cooperating manner, the rotor housing is constructed and arranged with a molded plastic, generally cylindrical projection which is designed and arranged to receive the channel portion so as to create a fluid-tight, sealed interface at the location of contact between the projection and the channel portion.