Augustine, "City of God," Book XVI, Chapter 26
And thus, because circumcision was the sign of regeneration, and the infant, on account of the original sin by which God’s covenant was first broken, was not undeservedly to lose his generation unless delivered by regeneration, these divine words are to be understood as if it had been said, Whoever is not born again, that soul shall perish from his people, because he hath broken my covenant, since he also has sinned in Adam with all others. For had He said, Because he hath broken this my covenant, He would have compelled us to understand by it only this of circumcision; but since He has not expressly said what covenant the infant has broken, we are free to understand Him as speaking of that covenant of which the breach can be ascribed to an infant. Yet if any one contends that it is said of nothing else than circumcision, that in it the infant has broken the covenant of God because, he is not circumcised, he must seek some method of explanation by which it may be understood without absurdity (such as this) that he has broken the covenant, because it has been broken in him although not by him. Yet in this case also it is to be observed that the soul of the infant, being guilty of no sin of neglect against itself, would perish unjustly, unless original sin rendered it obnoxious to punishment.
While many "Orthodox" folks may deny the doctrine of original sin, most - if not all - baptize their infants, maintaining the doctrine cloaked in liturgy whose meaning they do not completely understand.
Furthermore, not all "Orthodox" folks deny the doctrine of original sin (link - not recommended for its doctrinal content, just provided as an example: especially this particular link confuses guilt ipse with the feeling or awareness of guilt), and the same "Orthodox" folks note that baptism (including infant baptism) is intended to remit sin, including original sin (link - again, not recommended for its doctrinal content, just provided as an example).
Finally, the underlying concept is locked into the traditional liturgical post-baptismal/chrismal prayer:
Blessed are You, O Lord God Almighty, Source of all good things, Sun of Righteousness, who did shed forth upon them that were in darkness the light of salvation, through the revelation of Your Only-begotten Son and our God; and who have given to us, unworthy though we be, blessed purification through hallowed water, and divine sanctification through life-creating Chrismation; who now, also have been graciously pleased to regenerate Your servant that has newly received Illumination, by water and the Spirit, and do grant unto him/her remission of sins, whether voluntary or involuntary. Do You, the same Master, compassionate King of kings, grant also unto him/her the seal of the gift of Your holy, and almighty, and adorable Spirit, and participation in the holy Body and precious Blood of Your Christ.
(source - similar caveats to the forgoing)
But, as I noted to Gene, although many doctrines may have been locked into the liturgy in various ways, some were locked in more openly or more obscurely than others. For example, note that the prayer asks for forgiveness of "involuntary" sins. Yet talking to a typical lay Orthodox person, especially a "convert" from an Arminian (and KoD will probably whack me over the head with a rubber mallet for using this term too broadly, so I add:) or quasi-Arminian background, you will likely hear the typical "free will" rhetoric as it relates to the nature of sin, and so forth. You especially see this in comments that object to inherited guilt of Adam's sin, which cannot possibly be said to be directly voluntary by any of his seed.
This post is not intended to endorse the sect of Orthodoxy, nor its particular Baptismal liturgy, nor to mock Orthodoxy or its liturgy either. The point is simply to note that there is a legitimate argument from tradition that parallels the argument from Scripture on the issue of Original Sin, as well as on the issue of free will. We could even go to the issue of Baptism, but we won't.
P.S. Lucian, as a self-professed "Orthodox" I realize you will be tempted to jump in immediately. Resist the urge. Wait 'till the end of the week, and then - if you like - explain the errors you believe my presentation has. If you do so respectfully and cogently, many may learn something!