I think mix of Glowworm and Valliant parts ..
This is what I'd do ... Without it running ...
Check charge pressure of the Pressure vessel is ok.
Crank the pressure up to just under 3 bar .. and check discharge pipe again.
Pressure relief 'might' be weeping .. that will create a bigger leak at discharge pipe or seal it. You then make decision if it stops leaking .. to monitor it with bag or a johnny over the discharge pipe. If still leaking replace PRValve. I think part no may be 0020010153 £20-ish . Pressure vessel up to £105.
Take opportunity to leak check rest of system .. especially lockshield spindles.
Reset pressure to about ,7bar cold, no more than about 1,2 hot.
GL Al.