My C230 has started shifting vents from middle to defrost when the car shifts the lower gears. I am looking for some pictures of the location of the vacuum solenoids to find the leak. I have diagrams but they just show floating parts.

Defrost is the default for a loss of vacuum. My 97 C280 has electronic controls with buttons / display. Do you have the same or knobs?

At the rear of the engine and running to the passenger side, there is a main engine harness, in the harness there is a hard white vacuum line, follow this towards the engine to find the vacuum source / look for failed rubber hose.

I'd not sure if these systems have a vacuum tank or not, regardless there should be a check valve to keep vacuum in the HVAC side of the system.

You could have a leak under the dash but I don't have any diagrams.