so, when the car was off, blew some compressed air at around 15+ psi down the vacuum lines, no obvious leaks of any kind (air rushing out of some hole).
removed and refitted the
BOV vacuum line, removed and refitted the defi guage vacuum measurement line (enters the manifold at the front left - if your looking at it from under the bonnet).
took the car for a spin after this, and it no longer hits its desired 18psi, it boosts to 15psi now.
2nd gear drops from 15 to 11ish psi, the rest hold 14/15 psi fine (1/3/4).
any thoughts?