Is there an easy way to un-root Android 2.2 on Droid X rooted via z4root? Is there an easy way to un-root Android 2.2 on Droid X rooted via z4root?

The reason is that I would like to apply a Gingerbread 2.3 update from Verizon, and that update ALWAYS fails to install.

Since I never had a custom ROM on the phone, my first guess is that the problem may be due to being rooted, but I don't see an "Unroot" option in z4root.

Please note that factory reset is NOT an answer I'm looking for.
z4root added an "Unroot" button in version 1.2. Version 1.3 added "force unroot" (not entirely sure what that means). You can grab the most recent version from the XDA thread, then you should be able to simply hit "Unroot" and be on your way.