Ah ok
Every time I have seen such a failure is when the car has had a shunt, the engine and gearbox try to lurch forward and the rubbers tear.
Have seen one where it did go forward and the prop spline joint disconnected.
the engine didn't get a chance to go that far forward when I broke it properly... there was a lorry in the way
I suspect that over time the rear seal has allowed oil to leak onto the rear mount, attacking the rubber, the final straw being a conversation with a Honda Civic last year, as it was still intact in January '13 when I changed the clutch last
Engine mount was the nearside one, and had previously fallen off
suspect again a combination of oil damage and strain, as the engine rocks to the offside under load
Perhaps noteworthy that the nearside engine mount was replaced by TVP when they last serviced the car at 96k...