Old time fabric boot, lashed and painted
Fabric boot cut and sewn to fit and then bedded in some goo and lashed with small stuff to the spar and the raised lip on the deck with some half hitches and then painted several times to waterproof. In teh future, as needed put some goo on any cracks and paint over it all. Goes without saying that surfaces to be painted should be clean and not shiny/glossy. Soap and water to clean/degrease and a scotchbrite pad to degloss and there you go. The spar and the deck lip that accepts the boot should be well painted before gooing down the boot and painting it.