New Gas Tank Sending Unit Leaks

The new lock rings and gaskets are junk. Even using an old lock ring I had issues with the standard gaskets. I started getting my gaskets from DMT, he makes them himself and they're a better fit than the normal chinese junk. http://www.ebay.com/itm/DMT-Mopar-57-91-A-B-C-Body-Fuel-Lock-Ring-Sending-Unit-to-Tank-Seal-/360751319879

Sometimes the lock rings get tweaked too, I usually adjust the tabs on them anyway. I also install them with a large set of channel lock pliers, its easier to control how the lock ring seats than tapping on it with a punch.