One thing it could be is twisted arm wiring.
If it's skating inwards you need to increase the bias, so maybe the wiring is wound the opposite way which is effectively "setting" your bias to "-2" or so before you start?
I had a similar thing with cardas wire in a Rega - I had to untwist it in the right direction (either c/w or anti c/w) in order to get the arm "neutral".
I think clockwise will pull it outwards and anti-clockwise winds it in, but you need to be looking at it to make sure, (which I'm not at the moment!).
If so, SME could sort it quite easily.