I am having issues wit hthe plastic fittings in my titanium shell/tube exchanger. When the system is working properly, it seems ok as the water in the plastic side is cool, but when something goes wrong, like my 3-way valve leaking, it gets very hot leaks. I was thinking perhaps I would be better with a metal-metal seal there. Not surewhat is out there in 1 1/2" from metal and how to get back to plastic. Do they even make a male adapter with a plastic transition? Or could I use some kind of metal union, still need a plastic transition though.