That's new, havent seen anything yet about the fuel regulator causing a no start.

Usually it causes a hard start when it lets pressure drop after engine is shut off, but not a total no-start. Maybe the diapragm is totally torn causing no pressure at all?

Not seen any pressure readings at the filter outlet, just at the shrader valve.

Regulator is by the filter IIRC and might be worthwhile to replace along with the fuel filter and call it part of preventive maintenance?

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04 X5 3.0i auto
03 X5 4.6is