a sealed rotary joint and method are described wherein a purge fluid is passed over a tube rotating within an end cap and through a ball bearing component of the joint . a vapor stream including a vaporized glass forming precursor entrained in an oxidizing carrier gas is passed into a rotating optical fiber preform tube through a housing supporting the ball bearing . a stream of the oxidizing carrier gas at a pressure greater than the pressure of the vapor stream can act as the purge fluid .