it's not often I feel the need to disagree with Paul, but the TDi engine is not crap and defenders are cheaper than Disco's! However, I do agree the TD5 is a better engine and Discoverys are a more comfortable, quieter beast!
My TDi defender has done 65k miles, the first 35k miles of which were in Africa (!). The only problems of note were the water pump gasket and a clutch. Oh and everything is still covered in sand!
Graham