There's actually only one exhaust solenoid on the system, at the front. Off the top of my head it's next to the pair of solenoids for distribution. I can't remember if it's its own part or bundled as part of the distribution solenoids, think it has a simple 2-wire connector. At the rear of the vehicle is another pair of DISTRIBUTION solenoids (packaged as a single part) that control the rear left/right distribution. If the car need to vent air out of the rear, it opens the distribution solenoid for the appropriate rear side, and the air returns up the single air line back to front where it escapes from the front exhaust solenoid. The car can vent any corner using a clever combination of shutting the other three corners and opening one corner while simultaneously opening the only exhaust solenoid.
So if you genuinely do have an exhaust solenoid problem, it's at the front.
That being said, if the system is seeing correct heights all round then it should not need to add any more air or vent it, so I would wonder whether your problem is actually incorrectly adjusted height sensors, especially as you have stated that you have messed with them. They should all have their arms flat (horizontal) when the car is on level ground and the car is "happy" with its height. That assumes "High" is not selected on dashboard.
If your parking spot is on a slope or very uneven then it's theoretically possible that the car tries to compensate for a weird weight distribution there and add air to try and level the car, then when you pull away onto level ground it realises it has too much air and need to drop but can't because of a faulty exhaust valve I guess. However, definitely check the sensor arms are horizontal first, as that's a simple visual check you can do in any flat place which can be interpreted to tell you where to check next before you make another expensive purchase that doesn't help.
If an arm points upwards, that corner is low and the car should be trying to pump it up. If pointing downwards, that corner is high and the car should try and vent (unless it physically can't drop any more due to poor rod adjustment). If flat, car should be happy (even if rods are maladjusted, that's outside the scope).
Finally, you mentioned"C1725 Damping force control actuator" as well. The actuator is the little black stepper motor that twists onto the top of each strut when you install them, they control the damper of the strut, and twist a little motor inside when you select "Sport" mode. They're not usually problematic, so check you have twisted it back on properly and remembered to reattach the wiring for it.