Father John Crothers PP states in his letter (April AD2000) that the Pope has not declared his statement in Ordinatio Sacerdotalis to be infallible - the statement that the Church has no power to ordain women to the priesthood. It is true that he has not said whether he was exercising his personal infallibility in Ordinatio Sacerdotalis. But the teaching contained there is infallible.
This was stated by the Sacred Congregation for the Doctrine of the Faith on 28 October 1995, in a reply approved by the Pope, who ordered its publication. The Congregation declared that the doctrine has been set forth infallibly by the ordinary and universal magisterium.
As regards the authority of Ordinatio Sacerdotalis as such, all the requirements for an infallible teaching are fulfilled there.