A Catholic on sola scriptura

Gregory Daly writes intelligently and persuasively of the difficulties with the doctrine of sola scriptura as followed by most confessional protestants. More than 20 years ago I read an essay by the late Sheldon Vanauken, "The English Channel," published in New Oxford Review and subsequently appearing in his book, Under the Mercy. In it the author described his own spiritual journey from Canterbury to Rome and cited the same reasons Daly mentions in defence of his own evident commitment to Roman Catholicism.

In reading Daly and Vanauken I am almost persuaded. But not quite. If Rome were the only ecclesial body claiming custody, as it were, of the Great Tradition of which scripture is deemed a part, then it might be more convincing. However, given my paternal roots in Orthodoxy, I am aware that the Orthodox Church makes a similar claim for itself, namely, that its own authority determined the canon of scripture, the decisions of the ecumenical councils, &c. Yet Rome and Constantinople are at variance over a number of dogmatic issues, such as papal supremacy, the filioque in the Creed, purgatory, and a number of Marian dogmas such as the immaculate conception. Yet each claims the authority of the Great Tradition for its own formulations. Even Constantinople and Moscow differ over the precise extent of the Old Testament canon, with the latter tending towards the narrower Hebrew collection.

How then would one go about deciding between these conflicting claims? Who is right concerning the number of books in the Old Testament, about purgatory, &c.? Could the Reformation doctrine of sola scriptura, for all its difficulties, be a way of trying to reclaim an older tradition by which to measure the various local accretions claimed, albeit not incontestably, to be integral to the Great Tradition?