The OEM starters aren't any different than the ones you buy elsewhere. Basically they are a Bosch, Delco, etc with an equipment OEM's sticker put on it that means you pay $500 for a $150 starter. That being said it sounds like the starter may be hanging up as you start it and causing the percieved 'heat' problem. I've seen it happen a few times over the years, for various reasons, from burrs on the flywheel ring, to shorted wires causing it to engage while the engine was running. In either case the engine turning the starter will cause it to get extreemly hot. If your lucky if will start when it cools down, if not I have seen them 'blow the windings apart' and ruin the starter.
If the problem was on a B series Cummins I could tell you exactly what to look for as I've seen a problem on them on numerous occasions where a "will fit' starter is used that doesn't fit as well as it's claimed to. On a 3116 CAT I've worked on alot of equipment with that same engine and never seen one have a the problem your experiencing due simply to engine/exhaust heat. So, check your flywheel ring for screwed up places, insure the new starter has the correct gear in the bendix as the wrong one can one to hang up. Last but not least go over the wiring again to make sure there's not a problem there causing the starter to stay engaged that way. Good luck.