Flight Crew Air Transport Pilot (ATP)
Aircraft Equipment Problem Less Severe
Flight Crew Landed As Precaution; General Declared Emergency; General Maintenance Action
Aircraft
Eastbound the First Officer's oxygen mask failed. The mask was continuously leaking oxygen. This condition would have depleted the cockpit oxygen bottle at a rapid rate making it unsafe for an Atlantic crossing. After discussion with Dispatch and [Maintenance]; a decision to land at [a suitable airport] was made. An emergency  was declared. An overweight landing was executed. This aircraft also had a compromised braking system due to a placard on inoperable brake. We decided to dump fuel to increase performance margins. Maintenance replaced mask; completed overweight landing and ETOPS inspections.  We completed flight to [destination].  About 8;000 pounds of fuel was dumped at FL 340; about 30 minutes prior to landing.
[Narrative 2 had no additional information]
B767-300ER flight crew enroute to an Atlantic crossing reported they diverted to an enroute airport because of the First Officer's oxygen mask was leaking.