@dover I cleaned the manifold and checked each hole was clear, fairly early on.
It only sucked down at the beginning or end of an album, after I had manually moved the slider a reasonable distance and even then it was an intermittent fault.
As mentioned above, in my 3L pre tank, I have changed the filter material to half filled with 11mm ceramic beads, with 6mm BB gun plastic pellets on top. This seems to reduce pulsing a lot.
I don't like the idea of using cotton stuffing as this will have loose fibres that will need a very fine filter to prevent them getting through to the manifold and potentially blocking its fine holes.
Since using the new filter material, the slider has not stuck once, which is strange.
All working well and sounding great at present, the only thing I might try is a longer air tube from tank to Terminator. I have the Pump 5 inches (125mm) from the Tank as in the picture above. This allows me to unplug the figure 8 lead from the pump and the single 4mm outlet tube from the tank and move the whole set up as one. Handy for transporting to HiFi meetings.