I've installed a couple of the DIY drain plug kits. B&M markets them. The nylon washers are cheap. Replace the nylon washers with copper, put a drop of red loctite on the threads and tighten that thing down as much as possible. A wrap of teflon tape on the drain bolt will keep it from weeping. Be certain to check for clearance above the nut in the pan... you may not get it at the rear of the pan, but it will still be effective for draining the pan for removal. A nut welded on the outside of the pan is cheap and effective also.