You are correct, it should self center and may I clarify a bit further.

I have done a complete dissection of the distribution block. That picture has appeared here many times but it is not complete, there are 2 springs at either end of the piston which actually do the self centering.

If the piston shifts and will not return sometimes all that is needed is a light tapping on the block with a hammer.

There's a common misconception about leaking out at the switch. A leak cannot be fixed by any amount of tightening or even replacing of the switch. The switch is not designed to seal against the fluid pressure. That is done internally by the O rings. If there is a leak the distribution must be replaced or rebuilt.
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David Hunter