Didn't get much joy from the supplier, other than the to be expected "this has never happened before, we've sold thousands of them".
I have overcome the problem, I think, by putting what I considered to be an enormous bend in the vertical link. I not talking just straining it to insert the trunnion, rather I've "bent it"! Also, I've not used anything like the stated torque. 48 ft/lbs seems to me to be a hell of a lot, to the point where it started to overcome the bend I'd put in the sides of the link.
All seems to function okay. The various washers and the "O" rings are in place, but it still does not alter the fact that the tubes do not completely fill the bushes!
Comments please, Ken.