Oxygenics Showerhead Problem

We installed our showerhead a couple of years ago. We are now noticing that the pressure and amount of water delivered is about half from when it was new.
So far I have tested the pressure of the water coming to the fixture, that appears to be normal. Checked for a mis-shapen seal both at the showerhead and at the fixture connection, both normal. Soaked showerhead in white vinegar all day, that also did nothing.
Anybody run into this problem?
Do I need a new showerhead?