Maybe not epoxy based glue as it would be a bugger to remove afterwards. Pro-Seal do a range of Silicone based "Instant Gasket":
http://www.supergluecorp.com/pro-sea...-gasket-makers
Certain colours for differents applications, the black one would be suited to the fuel tank sender. Have used them quite a bit with no issues. Your local motor factors may have them in stock.
AndyH