Hi Larry,
It has always been considered that it is best to have a tube in. Why would Citroen go to the expense of fitting one, if they didn’t think it was necessary. The tube, provided it is fitted correctly, concentrates water around the valve guides to avoid them getting over-heated. The late Fred Annells insisted they should be fitted and actual reproduced them in brass, rather than the original steel; so I bow to his superior knowledge.