New sending unit leaks at lock ring

Just put a new fuel sending unit, gasket, and lock ring on my 67 Fury, and it leaks terribly at the lock ring. The ring is on as tight as it will go, and there is play in the sending unit when I grab the outlet tube and wiggle it. The gasket is sitting flush in its recess with no kinks or overlap, and the lock ring is turned to its limit. Any ideas what's going on here? Thanks.