Hi Richard.
As anyone done a leak back test on your car yet, if not get one done, also even though you the RAC says the UBFP is ok if you have less than a 1/4 tank of fuel it can struggle.
If you suspect the fuel rail sensor ? then drop mickyboy a PM and see if he can send you a good used one out asap, be best if you could get it on T4.
I presume this is the O-rings that Lee fitted to the regulator.
https://www.ebay.co.uk/itm/334135381254
I doubt he did a full refurb on the HPFP.
https://www.ebay.co.uk/itm/203408799927