OP here with a belated epilogue.

I returned the head to B&H a few days after my previous post here. They looked at it while I was overseas and found nothing wrong. It was, I think, simply overtightened to a degree that I was unwilling to challenge if it meant possibly voiding the warranty. B&H kindly held onto it until I returned from travelling and then shipped it back to me. They were helpful and straightforward throughout.

So, all ends well. Now it tilts. Time to find a camera to put on it. Thanks again to everyone for comments and suggestions.