Racor 500 O-Rings
Nothing is proprietary, not the o-rings, not the input/output ports. OK, maybe the beveled check valve gasket.
The fuel input/output ports are standard, straight J1926 (aka SAE-ORB, ORB, O-ring Boss) ports. See https://www.discounthydraulichose.com/sae-straight-thread-orb.html for examples. It's a straight thread with a slight bevel on the mating surfaces where an o-ring seals the mating surfaces.
The O-ring for input/output ports are standared BunaN o-ring, Dash #: 908 (Mcmaster part number: 9751K118) for the 3/4 x 16 ports (newer Racor 500)
All the gastkets/o-rings on a Racor are non-proprietary, one just needs to now where to find them. The all can be found on McMaster.com or, likely, where ever one can buy o-rings. I measured and tested the o-rings on my Racor 500 and found matching parts at McMasters.com.
O-rings (round and square) are standard and parts manufacturers design around the standard parts (o-rings, J1926 fittings, etc...).
Attached are reference documents, including a cross-reference for a Racor 500 and reference for the J1926 port standard..