I'm not and expert but I think that is a port to relieve pressure so diaphragm will flex. My pump didn't work, removed it and cleaned it up and saw the gold colored screen, it was plugged with oil and dirt. After cleaning it the pump worked just fine, saved a few bucks.
I think your diaphragm is cracked.
Gary
May 2015
I can answer this question...
john deere ls115 series 100 fuel pump is leaking ?