The leaks are rarely underground. Lets rule everything else out before you tackle that. 
The most common place for a suction leak is the pump baasket seal. I know you said it was clean and lubed but I'd check it again.
Another place are the drain plugs on the pump/basket.
I see that the suction line on the pump is out of plumb. I don't know if it's always been that way or not, but I'd run some water over the fitting on the pump basket and see if the air bubbles lessen while you're doing it.
If it did get moved, it could be broken where it goes underground.
The most common place for a suction leak is the pump baasket seal. I know you said it was clean and lubed but I'd check it again.
Another place are the drain plugs on the pump/basket.
I see that the suction line on the pump is out of plumb. I don't know if it's always been that way or not, but I'd run some water over the fitting on the pump basket and see if the air bubbles lessen while you're doing it.
If it did get moved, it could be broken where it goes underground.