I think you just need to reread your own words:
"...the sinlessness of Mary....now, i dont "not believe it"....that is, i understand the thinking process of the teaching and it makes sense to me...its just that i think so much of the teaching/tradition of Orthodoxy is rich for theological discussion and the enrichment of spirit and prayer life...but to require it for acceptance into the church?" (my emphasis)
Wouldn't you agree that it is beneficial to believe in a thing that enriches your spirit and prayer life?
If only "belief" were that easy!
I know many Christians today think of "belief" as a switch a person can turn and off at will, but I don't see faith that way at all. What you're saying sounds a bit like Pascal's Wager, which is in essence "I'll fake belief and trick God, and trick myself, that'll do it!"
One cannot force one's self to actually believe in something they do not believe in. They can trick everyone else, including their priest, and even convince themselves they "believe" it, but deep down if a person doesn't believe, they will know it in their heart. And certainly God will know if the person is merely faking belief in a doctrine, or if he/she sincerely believes it. This is the wisdom of Orthodox IMO, of not making every single doctrine a test of one's Orthodoxy. The test is the Creed, and participation in the life of the Church.
Of course what it comes down to might be what does one mean by "belief" to begin with? Historically "belief" meant something different than it has come to mean today. (mental ascension to various opinions of the world, God, and the afterlife) Faith and belief are not just holding ideas about something, but rather is something more akin to trust, commitment and just "living" you're life, and "being" Orthodox. If we start demanding mental ascension to various ideas that we've never asked people to ascend to before, that to me, seems a bit overly Western in thinking of faith and religion in general. Rather than being Orthodox, we worry about "thinking" about Orthodoxy. As though we can make neat and tidy boxes, put our way of life
into them, and then tell people here, "believe" this stuff, otherwise you're not one of us.
To put it more clearly what I'm trying to say, Orthodoxy is much more a way of being, that it is a way of thinking.
Now, it may be true that belief in sinlessness of the Theotokos is "advanced" Orthodoxy and thus is not required of all catechumens by every Orthodox priest. But, who is to say?
I'm not sure who is to say, but I am pretty sure it is not up to the individual whims of a parish priest to decide either. Each jurisdiction has it's own requirements, and one should adhere to those requirements, including the priests. Priests should not start demanding things of catechumen's based on their own personal piety, but on whatever guidelines are set forth by the Bishop, and the Bishop should follow the guidelines of one's jurisdiction.
I have always been taught, have always read, and have always learned that the issue of something like the sinlessness of Mary is not essential to being Orthodox. The Creed is supposed to be the bottom line...after all it is the Creed that we recite when we join the Church. We don't recite the Magnificat, or the Akathist hymn, but the Creed. If individual priests start demanding of catechumens more than the historic Church has asked of it's catechumen's then where is the submission to tradition, obedience and all the other nifty catch phrases we as Orthodox like to toss about?
So, it turns out that this little issue between you and your priest is so much more than a difference of opinion.
Indeed! It is much more than a difference of opinion. If the OP is portraying an accurate view of things, it seems to me, this priest may be overstepping his authority. I have never heard of a priest making this issue a requirement for conversion. Not that I'm have the corner on experiences within Orthodoxy, not by a long shot. But this to me just seems a bit, over zealous.
This is not a dogma of the Church. If a priest were to require this, what stops another priest from requiring the next potential convert to believe that Jesus was born without a placenta? that's part of Holy tradition as well, and has a history of support, but I don't believe it, even though my priest probably does. (though I've never asked him and he's never asked me, which is how it should be, personal piety is personal, not public IMO) Or perhaps a priest might make someone believe in Creationism before becoming Orthodox? Or perhaps priests might start making potential converts believe in Toll Houses, or other versions of what happens when we die. Some Orthodox believe in something close to purgatory, should we require that based on the whims of a priest? Or maybe other doctrines that are actually not required or necessary for Salvation, even though they might have a venerable and long history within the living tradition of the Church.
I do realize there is far more support for the sinlessness of Mary than for say, a literal 6 day creation, (which has little support in the Fathers actually) and I realize this is almost universally accepted in the Fathers, however the bottom line is it is NOT a dogma, not a pronouncement of the 7 Ecumenical Councils, and not in the Creed, so I just don't see how a priest can put this requirement upon someone. This just really seems like a scandalous requirement to me. As long as one not actively preaching against this doctrine, and as long as one is open to the possibility that it's true, I don't see why he would be so strict on this. Maybe there is something the OP has forgotten to mention. (perhaps he/she was hostile to the idea for a long while and he wants to be sure that hostility is gone?)
Or maybe this requirement is far more common that I'm aware of and I've just been exposed to a bunch of liberal priests in the upper midwest...lol! That could be the case as well. And I might be causing scandal to everyone else. if so, God forgive me!