sorry for lengthy post but i am baffled by bubbles.
my pool suddenly has more air bubbles coming out of one of the returns. I've historically had bubbles from that return for a little while after stopping and restarting the pump, but now it is continuous. Pool has three returns, but the bubbles come out only from one of them.
pool is inground gunite, about 40 years old.
I have a Superpump -- the body was new in 2018 (when i replaced the old motor with a variable speed) although the basket lid is old. I understand the basket lid seal is the most likely culprit. I have recently twice put in a new basket lid gasket, meticulously cleaning the gasket area and liberally applying Magic Lube (should i use Magic Lube 2 instead?) and tightening carefully, to no avail. I do see bubbles and churning in the basket, but historically i have always seen at least a little of that and not seen continuous bubbles at the return. It does look like there is more air in the basket after the pump has run at a lower speed than after it runs at higher speed, which i understand is a function of the higher speed causing more suction and pulling the lid down tighter. I have screwed the lid pretty darn finger tight, trying to keep both sides the same tightness. Is it possible to overtighten?
Attached photo of the edge of the basket and lid shows that on the left side there is a fraction of a millimeter gap between the lid and the pump body. I cannot get this gap to close. I have sprayed it with soapy water and i cannot see that water gets sucked in at this point. Should i try filling it in with Magic Lube?
Additional attached photo shows return lines with gate valves. These valves are probably 40 years old and i suspect them of adding to the air intrusion but cannot verify. I have closed them off one at a time and do not see any change in air in the basket. The valve stems have a little play; I have wrapped a thin plastic film (strip cut from shopping bag) where the stems meet the packing nuts and do not see any evidence of suction. The packing nuts do not seem loose, and due to their age i am hesitant to try tightening them, much less repacking them. Would it be worth trying to pack magic lube down into them?
The photo also shows threaded pvc connectors between the ground and the gate valves. I added these when i replaced the pump body in 2018. They seem nice and tight and i do not suspect them.
I have a sand filter with a Pac Fab/Pentair multiport valve; i replaced the valve top assembly in 2016 and i think it is ok. I have opened the air bleed and do not find air in the filter.
I might add that the pool seems to lose a little water from time to time, but it is sporadic and also baffling. I have run bucket tests with pump off and on and with plugging one skimmer at a time and cannot find a pattern. I temporarily lowered the water level below the skimmers and verified there is no leak in the pool shell itself. I wonder if there is something in the plumbing that is affected by varying moisture levels in the soil around the pool. I have a leak detection person coming in a few weeks.
Any advice?

my pool suddenly has more air bubbles coming out of one of the returns. I've historically had bubbles from that return for a little while after stopping and restarting the pump, but now it is continuous. Pool has three returns, but the bubbles come out only from one of them.
pool is inground gunite, about 40 years old.
I have a Superpump -- the body was new in 2018 (when i replaced the old motor with a variable speed) although the basket lid is old. I understand the basket lid seal is the most likely culprit. I have recently twice put in a new basket lid gasket, meticulously cleaning the gasket area and liberally applying Magic Lube (should i use Magic Lube 2 instead?) and tightening carefully, to no avail. I do see bubbles and churning in the basket, but historically i have always seen at least a little of that and not seen continuous bubbles at the return. It does look like there is more air in the basket after the pump has run at a lower speed than after it runs at higher speed, which i understand is a function of the higher speed causing more suction and pulling the lid down tighter. I have screwed the lid pretty darn finger tight, trying to keep both sides the same tightness. Is it possible to overtighten?
Attached photo of the edge of the basket and lid shows that on the left side there is a fraction of a millimeter gap between the lid and the pump body. I cannot get this gap to close. I have sprayed it with soapy water and i cannot see that water gets sucked in at this point. Should i try filling it in with Magic Lube?
Additional attached photo shows return lines with gate valves. These valves are probably 40 years old and i suspect them of adding to the air intrusion but cannot verify. I have closed them off one at a time and do not see any change in air in the basket. The valve stems have a little play; I have wrapped a thin plastic film (strip cut from shopping bag) where the stems meet the packing nuts and do not see any evidence of suction. The packing nuts do not seem loose, and due to their age i am hesitant to try tightening them, much less repacking them. Would it be worth trying to pack magic lube down into them?
The photo also shows threaded pvc connectors between the ground and the gate valves. I added these when i replaced the pump body in 2018. They seem nice and tight and i do not suspect them.
I have a sand filter with a Pac Fab/Pentair multiport valve; i replaced the valve top assembly in 2016 and i think it is ok. I have opened the air bleed and do not find air in the filter.
I might add that the pool seems to lose a little water from time to time, but it is sporadic and also baffling. I have run bucket tests with pump off and on and with plugging one skimmer at a time and cannot find a pattern. I temporarily lowered the water level below the skimmers and verified there is no leak in the pool shell itself. I wonder if there is something in the plumbing that is affected by varying moisture levels in the soil around the pool. I have a leak detection person coming in a few weeks.
Any advice?
