At 100 hours, you probably don't need to do anything. What you're seeing is most likely the fuel pump, I suspect--typically a metal cylindrical object with the fuel line going in and out and (if you look closely enough) wires to power the pump.
I don’t see anything, except buried in the back corner of the gen cabinet looks like maybe a metal one,, no clue how to get to it or with 100 hrs if I even need to
I don't know about a 2013 Onan, but when I had a 1996 there was a fuel filter. It was located at about where the fuel line enters the genny enclosure. I bought a new fuel filter, but sold the rig before I installed it.
Retired Anesthetist. LTP. Pilot with mechanic/inspection ratings. Between rigs right now.. Wife and daughter. Four cats which we must obey.