From what I was able to see, you have a .00001127° discrepancy somewhere. If you remove the mates between LA31 Top 400 and 'PART2', you can get the linkage to mate as expected. If you try to apply a concetric mate between those two parts, after mating the linkage, it won't go. If you measure between the top plane of 'PART2' and 'LA31 Top 400', you'll see the discrepancy. I didn't go any further than that, but that should get you closer.
Yes that has helped thanks, 'Part2' was an imported part from a .STEP file and must have had a face which was slightly off square, I rebuilt some parts and that has sorted it. many thanks for your help!