What does Avodas Avodah refer to?
Targum Yonasan: It refers to guarding. 3
Da'as Zekeinim, Hadar Zekeinim, Rosh: It is Shechitah, flaying and dissecting, Avodos of Kohanim [that a Zar may do].
QUESTIONS ON RASHI
Rashi writes that Avodas Avodah is Shir with cymbals. This implies that they may do so only until 50 years. Below (8:25), he says that after 50 he continues Avodah of Shirah!
Moshav Zekeinim citing Ri: We can distinguish instrumental Shir (it is only until 50) from verbal Shir. 1
Moshav Zekeinim (8:25): After 50, a man has more phlegm. This clogs chambers in the lungs, so his voice is not clear. Therefore, he ceases to sing. (If so, he cannot defend Rashi. Also below, he left Rashi difficult