I recentally had the gas tank, seat, carb off of my 1982 DT100 to make it operationl after many years being down.  Put it all together, fired it up, and it   But, when I shut it off I found two flat rubber pieces lying on the ground with no idea where they came from.  They are actually not quite flat with a slight "L" on one of the long sides.  They measure approx. 1" X 3/4" X 1/4".  There is a slight bulge closest to the angled end running down the long axis.  Any help would be appreciated.

Maybe they fell off the seat pan when you were handling it. Look at the underside and see if there are any witness marks from something that size and shape.

Or maybe they are the the ends of what used to be a rubber strap that holds the tool pouch in place. Those straps get rotten and often break. You may have just found the ends of the strap and the rest of it is long gone including the metal rings. That slight bulge might be what’s left of the portion that held the metal rings.

Greetings from Tennessee