Variation in the reproduction of the double tradition and an oral Q?

Recent critics of the thesis that Q was a documentary source have pointed to the variability in verbatim agreements between Matthew and Luke and argued that instances of low verbatim agreement point to an oral rather than a written 'q'. Careful examination of the ways in which ancient authors reproduced written sources, however, fails to demonstrate that authors had a consistent pattern of source-replication; in fact high variability is well attested in Diodorus' reproduction of Ephoros. The phenomenon of high variability in the reproduction of sources must be more carefully situated in the context of ancient scribal and rhetorical techniques rather than a facile appeal to 'oral tradition'.