Both front corners are saying, they don't sag to car too low in one day, but when I start the car the front jumps up massively
If it goes downwards when standing there, it should jump up as soon as you start the car - and maybe even faster in case, you touch the level button on dashboard. That is normal - that it "jumps" up..
But - if all is OK, it will not sag (go down) when standing. My CL 600 keeps it level at least a couple of months, that I have seen it now after the repair work I did for ABC.
Your car has leak on both front sides; it means that the both locking valves are leaking. That means that on the attached picture, the RED and YELLOW solenoids have O-rings leaking. You have to take them out and change the O-rings.
You can get good introduction from the link: https://www.abcspecialist.nl/uploads/documents/active_body_control_uk_2019_watermark.pdf#page=32
This video gives you good avises how to do it.
To open the solenoids, you should not raise the ABC system to the upmost height, but leave it to the 1st level. Then you have to lift the tyres from the ground and use jack stands to set the stable location for the car. Don't start the car that way. Start it only when the tyres are on ground. Pls note that if you have pressure inside the pipes, it will blow the solenoid out uncontrollable way - and you will get the hydraulic oil into your eyes!
You may get the solenoids out from the block even when the block is still in the car - not on the table, as seen on the video.
Change the oil and the filter. Work with white gloves - use clean tools!