But we Orthodox do not consider the Church Fathers to be infallible and untainted. No one is untainted. Even the Apostles were sinners.
The basis for our trust is known as the consensus patrum, that on which the Church as a whole agreed, based on the the Scripture and what the Church practices and believed since the beginning.
For example, St. Gregory of Nyssa was a student of Origen and shared with Origen the universal salvation belief (i.e. that all, including the damned, will eventually be saved), but the Church never consented to that. However, St. Gregory of Nyssa is one of the top Cappadocian Fathers of the early Church in other teachings to which the Church as a whole did consent.
The same is true of St. Augustine, whose works were practically unknown to the Greek-speaking Church in the East until the 15th century. When his works were finally translated the Orthodox Church rejected many of his teachings (the so-called "original sin" and total depravity for example), but still considers him a saint because of his other superb work and life, and because no matter what he wrote he always deferred to the Church and its collective understanding of the Scriptures.
The only way anything God gives us remains pristine is if we have no will of our own, bus simply act as God dictates.
Certainly, God gives each and every one of us a pristine soul. That soul, through our own defective will and fallen nature, becomes tainted. God certainly doesn't give us a defective soul.
In Hebrews 8, the New Testament writer reminds us that the First Covenant was made imperfect by idolatrous Jews. God's covenant with His people was perfect when it was given to Moses.
We are the source of corruption and change. God is perfect and unchanging. The Spirit moves us and leads us but He does not make us perfect.