Any competent modder can do it if all your parts fit properly and you have the gaskets. You never know where a leak is going to come from because greases shift, wear out, etc and so do the various gaskets. You just need to be sure the person assembling it has a proper tester and uses it. But I am with Nanuq, if you go to the trouble and expense to assemble a proper franken I would not take it swimming or in the shower. Gen vintage owners don't why should you with a franken.