Above (verse 17), it says "Al Dam ha'Asham" Why does it say here "Al Mekom Dam ha'Asham"?
Rashi: To teach us that he must place the oil on the location of the blood even if the blood has been wiped off, 1 since it is not the blood that counts, but the location. However, if the Kohen places the oil before placing the blood, it is invalid. (Rashi, Zevachim 43a)
Daf Al ha'Daf (Menachos 15b, citing R. Shlomo ha'Kohen): Why the Torah did not teach this Chidush above (in Pasuk 17) regarding Metzora Ashir? L'Chatchilah one should bring the oil the same day, and the blood is intact. An Ashir can do so. Often, an Oni cannot bring it the same day.