To use a more popular contemporary example I'll use a Justin Bieber song, say perhaps his popular hit baby featuring Ludacris. Now the popular chorus in that song is;
Baby, baby, baby, oh
Like baby, baby, baby, no
Like baby, baby, baby, oh
I thought you'd always be mine, mine
Now Justin Bieber has millions of fans all over the world who love him [each to their own] and sing his songs, know his song lyrics and all the dances. Imagine...I know its hard ..that a group of Justin Bierber fans met together weekly to talk about their love for him and would make a habit of singing his songs together as a group. But imagine this time someone in the group or a pair started to sing different lyrics and instead of the above sang instead;
Maybe, maybe, maybe, so
Like maybe, maybe, maybe so
Like maybe, maybe, maybe yo
You said you wouldn't mind, mind
Now we all know those bieberites would be on this like a honey badger would defend its kit [Baby honey badger]. They would in no uncertain terms let those who had changed what had been passed onto them through listening to the source of the lyrics that what they were repeating was incorrect. The strength of oral tradition is that the community protects the tradition [song lyrics in this case] from being changed because so many people are aware of what was faithfully passed onto them. The more people that know something the better it can be protected from change especially so in oral cultures where the information wasn't passed on in isolation but as part of a community.
What does this mean for the Oral Tradition of the Gospel?
In the same sense that the song lyrics are maintained, the gospels would have been passed on, memorised and protected by their community from change and especially so since they believed they were guarding and passing on Gods word. Remembering that unlike today where we rely on books and email to pass on and remember vital information. The first century Jewish community would have been highly proficient in the practice of retaining large amounts of oral information using specific mnemonics [memory aids] such as repeating something a certain amounts of times, and using music or rhyme which allowed many of the Rabbis and their students to eventually learn amounts of information we would today think almost impossible. In fact many of the devices used during that time are what many people spend thousands of pounds on at memory seminars to improve their memories today.
It should also be highlighted that that the community was not exclusively oral but was primarily so. The importance of highlighting the accuracy of oral tradition is important because many people today assume that because the gospel accounts were not written down for 25-60 years after Jesus death they must not be accurate. However as the example above demonstrates there are in fact some benefits to oral tradition that help to protect the message from change and actually perhaps have some merit over that of its written form.