Thanks again.  I'm still a bit uneasy with the way it's all worded, and really think ebay should improve this process, but it seems to be doing the trick.... i think.

It's still asking me to physically return it, but if i've understood you all correctly, i just leave it sitting like that for now, and i notice there is a "cancel return" button in the bottom corner so i'm guessing i can just press that when the replacement part arrives.