pump slowly losing prime
I have an in-ground pool with IntelliFlo VS-3050 pump. A few weeks back, I noticed that one of the returns was shooting water weaker than before and couldn't feel any water coming out from the other return. And when I checked the pump basket, the water level was very low. It was below the suction pipe and I could see water coming into the basket. The pump was still pumping the water, although weakly, so I guess technically it didn't completely lose the prime.
So I tried to re-prime the pump. After several attempts, I could fill the basket like 90-95% and there were air pockets on top. (Don't know why, but I had to try several times and rev up the pump up to 3000rpm to achieve that).
A few days later, I noticed that the water level went down again. I've been checking the web and asked around and I was told to clean up the o-ring (of the pump basket) and the surfaces it contacts. I did that three days ago. The water level is like 90% now but I noticed that it went down a little bit and it still looks like air is still coming in from somewhere.
Before suspecting air leaks in other areas, I'd like to rule out the pump lid/o-ring first. During the last re-prime, I didn't put any lube to the o-ring as the user manual says not to do that because the original o-ring contains a permanent internal lubricant. But would you actually recommend putting something to make sure no leaks there? I have lithium general purpose lube. Will that work? Or should I put anything special?