Did this test and vacuum is applied when revved so solenoid is working.

I also disconnected the EGR feed pipe from the intake so I could test it's operation - on idle there is no exhaust gas escape, then at low revs it opens and then closes again at higher revs so it is working as it should and not open on idle.

I still maintain that with constant vac to the mounts, it drove extremely well at any speeds above idle. It is not so smooth when the mounts are connected to the control solenoid...

They will have to change the engine mounts and take it from there.

So bad or faint are your vibrations - do you feel them in the floor and dash on both sides of the car? I do, but easiest to feel in the wheel as that is where hands are.

Do yours feel like a misfire (inconsistent judder) or is it a totally consistent vibration/rumble?

I expect some vibration from a diesel but I tested an identical age/mileage car and it had much much less than mine.