Found the reason for so many air bubbles.

This is my first pool (built in 1986) and all the return lines into the pool had lots of air bubbles.

At each valve switch going into the pump there is a tiny hole that is marked 'grease' and air is being sucked into the lines here. When I put my finger over the holes the air bubbles stopped but then the pressure gauge on the DE filter went from around 22 to 35.

So first of all, why are there grease holes (from their location the only thing they will grease is the water in the lines, not the valves themselves)?

Second, why are they allowing air to be sucked into the lines, or are they just worn out and need to be replaced?

Third, is the pressure increase from stopping the air flow something I need to attend to?