Revert from MIUI to Motoblur
There is this tool called RSD Lite, which is (AFAIK) an internal tool from motorola to flash their phones. You should be able to find it around the googles. 

And here you should be able to pick up a stock firmware for the Defy.

This method worked for my Moto Cliq XT, but don't let this be a  guarantee for your Defy!