All is now well and sorted!
No leaks, New Heating Element, OPV subsystem overhauled, multiple new gaskets; now beautifully clean inside and out, descaled, tuned up and delivering fantastic shots as if a new machine.
Thank you all who helped me solve the problems on my Synchronika. The T piece is a design flaw to keep an eye on in future, but the rest of it was clearly my own ignorance in using inappropriate bottled water causing some limescale.
I’ve now changed to Ashbeck, and bought some BWT resin bags for my reservoir to better manage the problem.
What a great community this is.
And Dave, please let me know by PM when and how I can chip in a few bob for the forum kitty.