To rebuild or replace...oil pump

Melling M72K (rebuild kit) is a buck less than the entire new M72 pump! Who rebuilds these things? And what does a bad pumps rotors look like, just worn gaps or grooves from injested crap?> I took my barnyard find 273's oil pump apart and saw some pretty good scoring on the tips of the 4 lobe inner rotor but the outer rotor looks perfect inside and out, and the .63 cent O-ring was rock hard and shrunk to expose 2 3mm gaps. I also noticed the outer rotor had coke at the base of each of its 'troughs', like the inner lobes never reached down there. I always just spent the money on new ones, just wondering how many I tossed that were still good enough? Not interested in HV model but I understand there was a kit that had extended rotors and cap back then too.