If it takes that much longer when locked then you do have a valve problem. Since the car goes down so quick I would probably locate the return lines from the two height valves (at the master valve) and remove them and catch the back flow. One should be distinctly larger than the other. If it doesn't seem to be, try leaving the master height control valve in the low position and block the individual return lines one at a time. (The master valve is blocking both when it makes the leak take longer) The car should last more than two days so you need to also isolate the system pressure check valve and should probably replace the system accumulator (there are five accumulators, one for each strut and a systems one). The fact that your light came off and on tells me you aren't working with a large reserve of pressure.

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Steve Brotherton
Continental Imports
Gainesville FL
Bosch Master, ASE Master, L1
33 years MB technician