Replaced passanger drive shaft seal and leaked again. Why?

Are you sure the axle isn't worn allowing a small gap between it and the seal?

Over miles, the seal can actually wear a groove in the steel. He needs to use a micrometer to check wear on the shaft.

How much movement is there up and down with the shaft inserted and locked, when they get a bit of wear on the splines with age, they tend to become very sloppy and the seals do not take up, I have seen a few of these with older corollas and Camry's.

There will be a little movement, but ones that I have seen that have leaked expecially after new seals being fitted, there is a lot of movement, what may be happening as the shaft rotates, rather then turning on a parallel axis, it tends to become some what elliptical and the seal can't maintain pressure on the seal surface as it moves up and down.