1. Was there a time in Church history when there was wide spread; for want of a better term, sexual apostasy within the clergy?
2. What do you think the Church's response would have been if this had happened say at the time of Pius XII or before but, in the 20th century?
In answer to your first question--there is no data on this since records were not kept until modern times. But to answer your second question, there is no question in my mind that strong measures would have been taken by the preconciliar popes to eliminate the problem, including firing bishops and priests and reforming seminaries. Pius XII in particular kept a very tight ship.