IMO, this pitting is the result of overloading.  There might not be sufficient lubrication to handle the increased torque, or the material that the gears are made from might not be up to the job, or the tooth profile might not provide sufficient load bearing surface area to distribute the load.  It could be a combination of all three.

The transmission gears rely solely on oil thrown off the connecting rod bearing.  The gears don’t dip into the sump, and the pressure feed into the hollow shafts only provides oil to the bores of the gears.  None of that pressure fed oil is getting into the gear mesh.

The gears on the input shaft block the gears on the output shaft from the oil being thrown off the rod bearing.  The larger input gears (4th & 5th) operate at a much higher velocity due to their larger circumference.  At high speed, the velocity of the gear teeth is very high, and any oil that gets thrown onto the teeth must overcome high centrifugal force in order to stay on the teeth and run through the mesh.  At high speed the load is also highest, so the tooth pressure is at max.  The perfect storm.

The old 4-speed has gears that are more robust.  The teeth are wider and thicker.  If I’m lucky, the material they used in the old days was better (like maybe 4340 instead or 4130 or something like that).

I would be forever grateful if any of you with engines on the deck could take a peek into the trans.  You can see all the input gears through the opening in the case.  Do any of you have pits in your gears?  Are there pits like the ones shown in my pictures?  If you have pits, please post some photos, and maybe provide whatever history you have on the engine (4-speed, 5-speed, oil used, mileage, how it was operated, mods, etc.).

But the inside is pristine.

The slide needle looks great, no discernable wear.

The LCGP muffler is lookin a bit funky but I assure you it will polish up nicely.

The duplex rear pulley bearing is as smooth as the day I installed it, and it still looks good to.  Score one for the Chinese.

Oooooooops!  I missed the intake port epoxy.  The crack is pretty big now.  It hasn’t failed but it certainly deserves attention.  You can really see the crack.

If you're piling epoxy deep, you might want to use Rebar. If it is gonna be deep, I like layers. Press the first application onto the metal. Wet it. Wet it Good! ( Lyrics of an old song?), then continue to apply, let it cure,break the surface, get rid of all of it, and leave foot Tooth. Use forty grit, or meaner, Wet That, wet it good! Rinse,repeat. Considering all the things trying to bust it up, maybe some fine Hobby wire for rebar? Hobby shops that sell RC airplane stuff keep, what I call, piano wire. But without any lumps and bumps like rebar has, IDK how helpful it would be.
I put bondo on a Mack cabover, on the eyebrow over a headlight. Beat the flux offa coupla welding rods, and filled about an inch and a half dent. It survived the heat and cold of West Texas and the punishment of the oilfield roads for about five years without cracking. They retired the truck and that ended That experiment.

What is the max depth of your epoxy?
https://acrylgiessen.com/en/high-temperature-epoxy/#:~:text=High%20heat%20epoxy%
2C%20on%20the%20other%20hand%2C%20is,which%20enables%20the%20epoxy%20to%20withst
and%20high%20temperatures.

https://acrylgiessen.com/en/high-temperature-epoxy/#:~:text=High%20heat%20epo...


I know you're a lot better mechanic than I'm ever gonna be, I'm just trying to help.