Kevin,
With all the work you have already done with lube and new O-Rings, I'd want a second opinion.. I am in favor with having someone new come out..
The reason for my suggestion that it might be a flow issue because of a partially clogged suction line, or something partially plugged on the return side, was because the tech that come out obviously saw what he thinks is cavitation. If the pump can't suck enough water that is what you get.
For me, troubleshooting is eliminating possibilities..
You have unions on your pump and filter, so it would be interesting to see what happened if you just disconnected the filter and let the pump run for a few seconds to see what kind of flow you have and if all the bubble get sucked right out of the basket area. You can rotate the pipe between the pump and the filter so that it would not dump water on the pump motor.
It would also confirm if you have any obstruction in the skimmer line.
Obviously, you can't run that way to long without dropping the water below the mouth of the skimmer.
Thanks,
Jim R.