There are many ways to stop leaks at the cooler fittings. remove them and replace the o-rings. Use new tubes - it is just 5/16" steel fuel line. If you need longer length than you can find there are unions that allow you to screw two lines together. Switching to after-market fittings and metal lines is a more expensive alternative but you might find that JIC fittings are more robust - they are made to handle 3000+ psi.
