Please allow me to provide some needed background.
First, the obvious: everything that's in big-T tradition is the common patrimony of both the Orthodox and the Catholics, since the Orthodox WERE Catholics --- and the Catholics WERE Orthodox (that is a paradoxical way of saying, we were all in communion with each other) --- for a millennium.
(Note: You seem to have the Byzantines mixed with the Orthodox. Byzantines are now Catholics, Orthodox are not. In any case, the whole lot of us were together for 1000 years.)
The constitutive elements of Big-T Tradition are the same in Greek and Latin, East and West.
The main elements of Apostolic Tradition are these:
- Of first importance: the writing, transmission, and Canon of the Scriptures themselves
- Apostolic Succession and hierarchical structure (Bishops, Priests, Deacons)
- Liturgical prayer, esp. the Holy Sacrifice of the Mass/Divine Liturgy and Eucharistic realism
- Spiritual life nourished by the Sacraments
- Ceaseless mutual sharing of spiritual goods in the Communion of Saints. Another way to say that is, the constant and necessary interdependence of the members of the Mystical Body of Christ
- Honoring of the Saints and of Mary, benefiting from their intercession (see "Mystical Body of Christ")
- Our own constant intercession benefiting the living and the dead (see "Mystical Body of Christ"!)
- Incarnational/Sacramental view of reality
- Confidence in the Holy Spirit's guidance of the Church (as guaranteed by the promise of Christ) and thus the authority and holiness of her official doctrines
That constitutes a preliminary outline of what comprises capital-T Tradition.
Keep in mind that the early creeds and synods, and the Nicene Council, historically *preceded* the canon of Scripture.
Read that again: the creeds preceded the canon of Scripture.
Do you understand what that means? It means the canon was formed based on what the Church already believed in her creeds: these creeds provided the criteria which tested and verified the authenticity of various purported Scriptures (and not vice-versa).
Therefore to accept Scripture is to accept Tradition.
Hit the delete button on Tradition, and Scripture disappears from your screen.
The creeds are a good way to "see" the content. Orthodoxy and Catholicism have the Creeds (Apostles Creed, Nicene-Constantinopolitan Creed, Athanasian Creed) in common, as well as the first seven Ecumenical Councils and all the Fathers of the Church from the first millennium of Christianity.
As for Immaculate Conception: consider Mary as Immaculata and as Panagia. Different languages, similar devotion. I see here convergence, not basic disagreement.
