"The blade in question had replaced the old one that stopped working..while the aircraft was approaching NRT on the previous leg."
Thus we can assume it was raining on the previous sector.
During turnaround apparently the faulty blade was replaced - one would assume that the problem was entered in the Tech Log and subsequently cleared, and that the crew then checked the repair.
Therefore wipers serviceable again.
"We saw the captain-side wiper blade bending upward about 10 minutes after takeoff from NRT."
So was it raining on departure Narita, such that the wipers were used for take-off, causing the problem to recur?
If so, why was it okay to land back at NRT in the rain, but not proceed to Vancouver where rain was forecast?
Is YVR Cat iii certified?
The wipers on the Capt's and F/O's side, on the 747, are operated by 2 independent motors (one for each side), so there should be a CB for each motor, meaning the Capt's side could have been isolated leaving the F/O's side serviceable.
But hey, money is NO PROBLEM for JAL. Nothing is ever repaired - it's replaced!