There is no washer under the rear planet because it sits in the grooves and contacts gear steel on the wear surface.
In other words it doesn't need one there and it'll mess up your end play if you put one in.
Looks like one belongs in there though doesn't it?
Try putting your front washer under the planet and you will see how the planet won't go in all the way like it is supposed to.
"missing two seals on the shaft" has me wondering though.
What do you mean by that? (Picture?)