It has taken a long time to get this wrapped up, not only for the troubleshooting, but also the time to get in parts, and removal of the hub and pulley required cutting them off after untold wasted hours trying separate them without destroying them. Finally, yesterday, the new hub and pulley arrived, I got the old pump out and the new one in. Performance is restored. The left wheel had been weak for so long that I had become used to it, and it was pure joy to feel the snappy response with the new pump. It did make me notice, however, that the left side now seems to have slightly more power than the right, so I may be repeating this for the right side before long.