Have you noticed that the ONLY sites which purport to be Marian apparitions that have been 'approved' by the Church are those at which Jesus IS glorified, and are ones where people are led TO Christ? There are a lot of kooks in the world, and one can claim any sort of 'apparition', but the Church is very wary about putting any store in the claims before some diligent research. If Mary is helping to lead God's people, she would be leading them TO Him, not away from Him. As for the title of Co-Redemptrix; it is simply a statement of the fact that Mary was an active participant in the Redemption of man by virtue of her "Yes" to God's invitation to be that "Woman of the Promise", foretold in prophesy. It was she who brought forth Jesus into this world, as the Father had planned, so she is an important figure in our Redemption. The Church does not teach that she did the redeeming, only that she was the one who God chose to make it possible for us.
Catholics venerate and honor Mary, as led by Jesus's own example; we do not worship her. As for the 'tradition' not being explicitly in the Bible, and thus you find it difficult to accept, what about the teachings of Jesus that ARE explicit in the Word of God that you don't accept, such as the primacy of Peter, and the Real Presence?
We could bandy Scripture about all day long, but as far as tradition is concerned, I'll take the word of folks who were with Mary while she was alive, and who passed her story along to those Church fathers who DID keep her story alive for the successive generations. They didn't make it up out of whole cloth a millenia later; they continued her story from its inception. As for the idea that Mary couldn't possibly have been conceived without sin, I personally believe that anything is possible with God, and if He wanted the mother of His Son to be sinless, so as to be a worthy vessel, He certainly could have done so. Far be it from me to put any limits on what He can do. And as was pointed out before, Christ was fully human, as well as fully Divine, yet he was also born without sin.
Nonsense...they did not pass along any story of Mary's sinlessness.
As for the title of Co-Redemptrix; it is simply a statement of the fact that Mary was an active participant
No, "co" implies equality whenever it is used (as in co-ruler or co-op or co-sign). "Co" never implies simply an aide.
Yes, she was a participant in God's plan as was Abraham. But he is not considered a co-redemptrix. That was a very unfortunate term for the RCC to assign a created woman.