OK, after rebuilding a couple of Revo trannys now, I think I have a winning combination. I noticed that whenever a pin broke, it was right where the threads meet the shaft, so that must mean that that spot is the most stressed. So, I modified two of the stock pins so they are about 7mm long each and then threaded both screws on each side of the gear hubs so the shaft tips meet inside the shaft. Below is a pic of the modified screw pin:
When cutting the black FOC pins and the original chrome pins (same size, diff color), the black ones seemed to take longer to cut with the dremel, so I think they are harder.
Also, this mod has an added benefit: Since both sides are now captured, if a pin
does break, the broken end won't fall out and mess up the other gears.
Each of the three shafts are different in diameter, so there is easy no "one fix for all" solution. So...
Input shaft: In the gear hub, drill out the side of the gear hub using a 7/64" drill bit to allow for the screw pin threads. Modify two of the stock chrome pins like in the picture above and screw them in. The chrome ones are OK to use here because the pins have less force being exerted on them due to the gearing.
Idler/middle shaft: Basically do the same thing as the previous step, but use two of the black FOC pins instead. The pins here need the extra strength.
Output shaft: Since the output shaft is a softer metal, and has enough diameter, drill out the shaft hole to 2.5mm and use a Revo out drive pin.
I torture tested this setup a couple days ago and it seems to be holding up better.