Nothing special, just used little Epoxy cups (10 packets in a can, with short pop sickle sticks)

 I believe it was 3M or Loctite brand (you just remove cover of one epoxy cup, use stick to push down on cup, then start mixing the White and the Black together = makes Gray mixture, then plaster the epoxy, into a CLEAN  and DRY bore, and roughly smooth it with that stick. You only have about 10 minutes or so to work with it, before it gets too stiff. We usually let it set overnight, but if a guy was in a hurry, you could put a trouble light (light bulb) down in the bore to help it cure quicker; then you could start hand sanding, sooner.

Note: really small pits, the epoxy may not stick good enough and just comes off, when sanding = don't be alarmed, those really smaller pits aren't going to hurt anything =you are after fixing those big pits, that probably are big enough that a new liner O-ring has no chance of sealing, unless something was done to improve the surface.

Also, if you sand, too much (or too coarse of paper), and a chunk happen to come out, just reclean the area,  re-epoxy it and let it dry (start over, again, basically) Your fingers, can tell you a lot, by feel, about the curve and smoothness.