Thanks Colin and David,
A felt 'ring' around the turret base makes sense. It would make an enormous difference to the ingress of dust, yet still be soft & flexible enough not to impede the rotation.
I'm familiar with the turret clamping arrangements for Cent and Leopard AS1, so can visualize what you are describing for the little Vickers. All makes sense.
Looking forward to the next installment of 'Tank Tales'!
Mike