The Torah specified that one of the male sheep is an Asham. It did not say if the other male sheep is the Chatas or Olah (verses 19-20)!!
Rashi: The ewe is brought as a Chatas. Ramban, Moshav Zekenim - the Torah already taught that Olah is always male, and Chatas [of a commoner] is female.
What purpose did the three tenths of an Eifah serve?
Rashi: One tenth of an Eifah accompanied each of the three Korbanos. 1
Moshav Zekenim: The three sheep, three Esronim and one Log, seven in all, hint that he should engage in the seven Chumashim; refer to 14:7:151:1.
Even though no other Chatas requires Minchas Nesachim.
What purpose did the extra Log of oil serve?
Rashi: To sprinkle from it on the Metzora and to place some of it on the middle joint of his right ear and on his right thumb and big toe.