Another perfect example for the use of a borescope. Someone just used one to remove a screw that had fallen into a spark plug hole and if I remember right, that person rented the 'scope from Home Depot or similar. Let the level in the tank drop, put the borescope in the tank and look around inside until you find it and then use some type of flexible retrieval device (the ones with the multiple expanding 'fingers' would probably work best) to retrieve the gasket.
Even if you pull the tank you probably won't be able to get that piece of debris out of it until you remove the fuel pump, and even then it might be a challenge. Of course if you are persistent you should be successful but the borescope sounds easier, faster and a lot more fun....
Maybe what we really need is a traveling borescope / retrieval service. Someone to come directly to your house or place of business and retrieve whatever you lost in an orifice.... well, not just any orifice but the ones found on motorcycles should be OK.
Brian
It is a paper seal with a foil backing, and of course it is a full tank of fuel. I guess ill will look into removing the fuel tank over the winter. Thanks for your help.