[Flathead Fever]

That black material looks similar to what modern cars use. The old cork float eventually sinks. Even the brass ones that are two pieces of brass soldered together develop tiny pin holes and sink. I was a mechanic for the phone company and every few years I'd have to pull out the sending units and replace the brass floats on the Ford F-600s, it was so common I kept a couple of them in stock. They'd fill-up with fuel and sink. The new style sending units seem to be really good. The electric in-tank fuel pumps fail around 100,000 so now the floats outlast the pumps.