Fuel Pressure gauges can be bought in tuning shops for about 30 to 40 quid.

Just plumb them into the fuel rail and compare the readings with those in the manual.

If they are too high, the regulator is at fault, but I wouldn't advocate changing it "just in case" because it's failure needs to be proved first.

You can bankrupt yourself by throwing parts at the problem.

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Paul Gibbons
'93 320CE
'73 Jensen Interceptor (Resting)
Giant Full Sus Mountain Bike