Badger, George Percy. 1852. The Nestorians and their Rituals. Google Books
This seems to indicate that there may be ruins of Maqlub Mountain itself, or there was a misunderstanding — opposite of versus opposite from — as the current location is actually on a mountain opposite from Maqlub.
On the opposite side of the mountain [where Saint Matthew Monastery is located], are the ruins of an ancient monastery dedicated to Mar Auraha, which once belonged to the Nestorians, but is now claimed by the Jacobites. Badger 1852, p 98