As a new boy I'm not sure where/how to reply to individual posts. So thanks to Pete & Paul for your comments.
Paul, some years ago in the early part of my restoration I did use the Frost product of the time for sealing fuel tanks. However, I have heard since that this product was not proof against ethanol and there was a risk of a reaction with the sealant. I've done very little mileage since so I'm reluctant to apply a another sealant over the top of one that may not be secure. Thanks for your comments.
Pete, thanks for your comments. The workshop manual doesn't show the detail of the top pipe entry and I can't quite see how to remove it to check on the sealing arrangement. I can just see a nut under the reserve lever - is this the means of removal of the lever and pipe assy?