We have to understand the Churchs perspective on homosexuality in order to understand her position.
She holds to the truth regarding human sexuality, that with prayer, fasting, good works, self knowledge and obedience, a persons life in the spirit frees him enough from his primal nature to truly be a spiritual father to his flock. This goes for heterosexual and homosexual tendencies. It’s called affective maturity.
So when she says that those with ‘deep seated’ homosexual tendencies are not to be admitted to the seminary or Priesthood, she refers to those struggling to resist against those urges. That’s a sign of lack of affective maturity. Having worked towards this affective maturity and having lived 3 years without that slavish struggle, it is possible that a man could be admitted to the seminary. He would realise that prayer, fasting and receiving the sacraments continue to spiritually strengthen him against slipping back.