Well not to second guess you, but it seems like engine assy lube is overkill. I only bring this up because you were talking about rotating mass. How would rotating mass be an issue if you're running tar in your gearbox?
The failure I had was purely shifting under too much throttle, the gears are all flawless otherwise. I would have taken pics but the truck is back together. The nylon gears all had a nice square apex, and NO signs of wear. I know the original Maxxes ran the trans dry, which makes for a powdery mess the first time it's split. But it was greased for a few years, then I switched to STP about a year ago. The only other time the trans had to come apart was when I sheared the rollpin on the input shaft. Did a solid pin as well, with about a .002" taper. Banged them in with a railroad mallet and green loctited.
I also use a spool in mine, and that puts quite a bit more stress on things. The trans has been the least of my worries, I have destroyed 2 MIP bones and 3 of my own drives, one steel and two titanium, all with plastic lower gears... mine weighs 15 pounds now with a rubber front bumper, and goes like a 10 pound truck. The real weak point is the damned rear pinion. I always curse at them for putting the two little 6x12 bearings so close together. If they'd have extended the distance in between by even 8 or 10 mm there would be significantly fewer bearing and mesh problems. Even with an alloy diff case, there is just too much rock in the pinion axis, and it quickly eats itself.
That's one thing STP can't cure....