I have a 2003 E500 Sport. My fuel gauge has been acting up lately. When I start the car in the morning it will give me a certain level ex: (A little above quarter tank) then I'll drive to my destination. It will now say a little below quarter tank. Then I'll go back into the car, start it and it will say above quarter tank then when I get to my other destination. It will say below quarter tank again.

It completely passed the point of actually being on quarter tank for any given time. It just fluctuates every now and then. I thought maybe my car was just drinking more fuel than it usually does but I'm leaning towards believing this may be a gauge problem. Any ideas on what could be wrong?