Would be nice if someone could explain exactly how the system works. From my understanding, the compressor pushes it to the front and rear reservoirs, from where it then pushes it to each of the bags. As my rear bags hold perfectly, even with the car quite loaded, I want to say that the compressor (despite running for a bit longer and not being very silent) shouldn't be the issue. Since my fronts are both dropping at the same rate, it looks like the issue has to be at the front reservoir, like you had. I tried to get to it this morning, but I'm not sure I can figure out anything meaningful without taking it apart, which is currently out of the question as I don't have a second car available. I am considering risking it and ordering that valve you mentioned and just praying for the best (happens quite often with this car, yet I still love it to death).

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03.06 BMW X5 4.8is LeMans Blue