Fuel pump parts question

I was working on my 2006 YZFR6S, trying to get it started after long time sitting in the storage. Noticed that fuel pump is leaking from around secondary nipple (or whatever it’s called). Or is it return? Regardless it was little loose and dripping fuel from around. Upon closer inspection taking it apart there is an o-ring there that is all dried out. Tried finding replacement part number. Not having much luck. Neither with replacement fuel pump plastic casing. Would anyone have part number or recommendations on what to replace it with. Considering it’s gasoline, I am sure I can’t just go and pickup any matching o-ring. On similar note, might be silly question, but why is there return line on this model. Fuel pump from another year looks identical but does not have that extra nipple. Do people ever convert their fuel pumps from let’s say R6 or R1 and just close off the other line? Obviously, I am no mechanic and don’t know much about it, but seems like a return line to me. See pictures below. One on the tank is from R6 or R1. Don’t recall. But this is just as picture referencing what I am talking about. I installed it temporarily while working on the original.