Hey Tubs,
There was a message string here a few years ago about whether cork needs to be coated to resist gasoline. Somebody posted there are two kinds of cork, depending on the type of cork plant used. There is open-cell cork, and closed-cell cork, and no good way to tell which you have except to do what you are doing. Open-cell cork needs to be coated or it will eventually sink, while closed-cell cork does not. Several years before that post, I took a cork from a wine bottle and put it in a gas tank uncoated. It sunk in about a month causing the gauge to read empty, so it was open-cell cork.
Dave
