To eliminate intake leaks just spray around it with WD40 when its running, if it picks up and runs better, voila.. you're laughing.

Servo pipe is that end of inlet too, have you blocked it off incase servo is leaking? Seen that on RS Turbos 'back in the day'

Have you checked the cam and lifters to make sure they're ok?

Done a compression test?

Back when I had a fringe, my S1 had starting issues and would flood the plugs, metering head cured it. Getting old now though so getting bits must be hard.