I looked in the right side of mine, the main tank, and I have that same notch in the lower corner of the baffle wall that is about 12" from the right side. My two plugs were already loosened by the PO and the screens and upper brass discs are gone. 
BTW one time my 120 quit on me and the reason turned out to be a buildup of very fine rust dust in that drain plug cup that was blocking off the pickup tube. It was not sucked up into the inline filter I had between it and the fuel pump, the filter was still clean.
I just finished restoring the sender, the tricky part being to lift the resistor out when its stuck with crud. I put 2 nylon zip ties around it and pried them up with a screwdriver. Then cleaned it in muriatic acid swimming pool cleaner. Very delicate work soldering the ground inside there. It reads 2.5 Ohms empty and 88 Ohms full.
