I listened VERY carefully. As a matter of fact, I received the Religion subject award my graduating year at Vancouver College. I remember full well what the party line theological reasoning was for the "stain" of original sin, and I could quote liturgical cliches like the one you did from memory. However, no explanation along the lines of 'propensity" changes the implicit supposition that an infant is born with the STAIN of Adam's original sin, and that one of the effects of Baptism is to wash this slate clean. If original sin truly had no PERSONAL component, there would be no need for the "repair" of baptism, as we all have the PROPENSITY to sin at all times in our lives, before, after, or in spite of Baptism.Obviously, you didn´t listen carefully to what your oh-so-catholic teachers told you about original sin. Neither has it anything to do with the OT "the sins of our fathers", nor is it anything like personal sin. We are born with the PROPENSITY to sin - not in a state of natural grace. OF COURSE we are born without personal sin. It also is the most obviously TRUE christian dogma.
I have heard the official explanations from more Brothers, Priests, and Monsignors than I care to remember. As with all things, When reasoning attributed to the Almighty sounds like bunk, I go with me.