the motor for the convertible top makes loud noise when being used. maybe oil?

Hello, The Z4 has an issue with the insulation around the motor preventing liquid from draining. It will cause lots of rust around the motor, and eventually cause the motor to fail. Remove the insulation (sound barrier) from around the pump motor, and see if the motor is covered in rust. It likely is, and is likely failing. Also, you may already be onto the solution, as there may just be a leak in the hydraulic lines allowing air into the system. I'd still check both, and check the regulator assembly for a comprehensive inspection.