The original bearings were both facing the same way which seemed wrong, so I turned one over. Actually I tried them both ways - back to back and front to front but get the same amount of float in either configuration. The spacer rings are OK and neither the nut or ballscrew is touching the seals. Chai has suggested I need to offset the bearing and/or ballscrew by 15 degrees. But that can't be right because the ballscrew would have to be a mile off centre to get that angle? However, based on that information I assumed that the bearings should NOT be perfectly square to the shaft, so shimmed the bottom only of the outer race with a 1/4 section of a 0.3mm shim washer and it seems to have done the trick. But it also feels like a bodge?!

I've never used AC bearings before but assume that the "back" is the side which is stamped with the bearing number (7001)? If so, that's how they are currently configured. Without the offset shim they gave me around 0.25mm of end float. The other way round was no better.