904 transmission fluid level

Does it matter if the fluid shows half an inch above the full line? No leaks present, no other issues.
I do believe that too full can cause aeration of the fluid.

Get a small dia hose and syphion out some fluid
It depends on how you check the level. Check it warm (operating temp) on a level surface, in neutral. Block the wheels so it doesn't roll away. You don't suction any out until you have properly checked the level.