The plate that seperates the two halves has telltale marks in it that indicates where a ball was, so if you do mess up its not too huge a deal.

You want to remove the valve body, remove the 2 screws holding the halves together(from the top) then hold it together while flipping it over, setting it so that the bottom of the valve body is facing up. Then you can pull the bottom of the valve body off and do your work.

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81 300SD daily driver/project
86 420SEL (sold)
85 380SE(in the graveyard)