fuel tank sending unit + o-ring
$200 shipped
per Mike: "factory ring is made from rubber that swells when in contact with gas, so forms a tight seal.
As was pointed out, it doesn't take much of a flaw in the old o-ring -- or if it's old, to allow gas seepage. And a little bit of gas will make a lotta smell in your trunk, which will make its way into the passenger compartment."