Air in pool return lines

[Pool in Carolina Blue]

Thanks Brad. I pulled the pump cover and the O-ring looks fine. I lube it every two weeks or so. However, when I turned the pump off, I noticed a slight water leak at the pvc connection to the pump. Not a lot of water, but a small leak nonetheless. It looks like to prior owner tried to "seal" it with some sort of gray colored liquid cement. Could this be the source of the air?

[duraleigh]

Could this be the source of the air?

If it's on the suction side of the pump....yes. If it's on the pressure side.....no