Yet his later books did not contain any error. Seems consistent with the claim of Hugh Akins, who knew Fr. Martin personally and says that he converted later in life.
Also, there's no proof that he was an adulterer.
There is proof. Later in life, he wrote a series of sensational books; as far as I know he never recanted any earlier writings. His book Jesus Now is blasphemous to say the least.
Where's the proof that he was an adulterer, then?
As for his earlier writings, I don't deny that they were trash, but Hugh Akins and Bernard Janzen - two credible sources - claim that he converted. So far, no one has been able to refute their claims. All they've been able to do is prove what Akins and Janzen admit, that Fr. Martin used to be a liberal Judaizer. That doesn't refute their claims that he converted, though.
If anyone can show me a clear heresy or blasphemy that Fr. Martin states in one of his later books, I'll retract my defense of him.