At make night Gerald was working fine for most of the evening,
In the last hour it started jumping along the y axis, in use and setup.
We had a look and the belts don't seem to be lose, and there wasn't anything else obviously wrong.
As it is it's unusable.
I think (I'll reopen this if there are more reports of problems with him today) that this is a duplicate of #287. The remaining screw for the shim had worked loose again, so I've re-tightened it.