No, you didn't. They only proclaimed themselves infallible with no support from scripture. I can assure you that a group that directly contradicts scripture is not infallible.
>>To date, I have not seen a reason to believe it is not.<<
Galatians 1:8 But though we, or an angel from heaven, preach any other gospel unto you than that which we have preached unto you, let him be accursed.
Now please show your infallible source that shows where the apostles taught the assumption of Mary and the requirement for it's belief.
Please show us where Paul was only talking about written texts? You can’t prove it so your argument is fundamentally flawed.