Hard to say what you're experiencing, based on that description. You do know that the head can be tilted on these? I'm attaching a document that might be helpful...
If it's the carriage that doesn't sit stable on the column, though, you won't find anything in this document - but I would expect that there are rollers in there that have some sort of adjustment to take out the play without binding. Looks to me as though the cover on the carriage can be taken off rather easily to get at such an adjustment (and the attachment of the counterbalance spring), but I haven't had mine off, so I'm really just guessing, here.
Be really careful if you do go inside the carriage! That spring is scary as hell...