Pretty sure that if there is a proportioning valve, it will be on the drivers side front strut tower.

On the later subaru models without EBD (electronic brake distribution), thats where it is. On models with EBD, the valve block is still there, but the insides are removed. So it still looks like the proprtioning valve. But if you open it up, its all free inside. On models with EBD, rear proportioning is handled inside the ABS modulator.

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Doing it for all the wagons out there