leak at sending unit

No need to reuse any old parts or make another gasket. This is a real common problem. All you have to do is look closely at the retainer ring for the sending unit. The "tangs" that tighten down on it as you turn it to secure it need to be carefully bent just a little bit before you install it. this puts the ring under more tension and causes it to compress the o-ring like it should. I've done it a good bit and it seals right up every time.