Chris, I have replaced the paddles on my WF440 several times, (why is another matter!) they are fitted from inside the drum. I seem to remember the original paddles may have been screwed in but I seem to remember the screws, again, were accessed from inside the drum. To fit new paddles you just drop them in the holes and slide them toward the back of the drum to lock them in place. Try sliding the loose one toward the front and see if it comes out. It may be tight so you need to pull/slide it really hard.
Rob the reluctant repairer
March 2009
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