Water Pump replacement - removal problem

Pulling my hair out here. Trying to pull the old water pump, but cannot get a tool in the 6mm Hex bolt on the back of the pump bolting to the block. Has anyone done this? The 13 mm on the front came out without a problem, but I've been trying to get this other bolt off for hours. Intake manifold in the way on the right, just a small hole between that and the water pump.

Pulling my hair out here.
Trying to pull the old water pump, but cannot get a tool in the 6mm Hex bolt on the back of the pump bolting to the block.
Has anyone done this? The 13 mm on the front came out without a problem, but I've been trying to get this other bolt off for hours.

Intake manifold in the way on the right, just a small hole between that and the water pump.

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