Barry,
If you want to respond to the other party's response, here's how---
Go to the ebay page:

http://cgi2.ebay.com/aw-cgi/eBayISAPI.dll?ReviewFeedbackLeft

Fill in you name & password. When the new page shows all the feedbacks you left, you will see an "envelope" icon on the one where the other party responded. By clicking on the envelope, you can leave a supplemental feedback like "Check arrived after all. All OK." or whatever you want to say.