Kindly put some more light on the old meaning of the word 'durood' and its use in ancient language.
I found the following meaning of the pahlavi word 'drod' in dictionary "A CONCISE PAHLAVI DICTIONARY" by MacKenzie
Page#50, drod : Health, well-being, prosperity, peace
and seems the use of the word (drwd) in the same meaning in the old text of Middle Persian era as shown in "Middle Persian and Parthian Manichæan Texts" (Please copy paste the link below to view the scripts)
Some more useful information regarding Pahlavi language history.
Thanks & Regards