Expensive repairs (Yes/No)?

[Jmac]

Sound like the non return valve is leaking back mate, but you must get someone who know K jet to check it, could be leaky injector, Accum ro the Check valve. Most of the time it is the check valve but still best to have the gauge on and watch what it is doing and when. If you fit a gauge with a tap then you can check system pressure for holding and also check engine side, this way you can rule out a dribbly injector.
Good luck, Kjet is good when its right so persevere, sorry to hear about the rest of the goings on
Jmac

[superfly.nn]

Yeah I have a replacement accumulator and a check valve is only $20 dollars so I'll get one of those too just in case. I know the fuel pump is ok pressure wise as I've had that checked.
I really want the car to be running perfectly before the German Autofest in September.