Okay, did some testing using three different M-03 chassis.
1. Newish grey chassis I've been running for a month
2. Really old RTR black chassis I used black gears in for a while
3. Brand spanking new black chassis
Here's what I've seen:
1. Grey - very minor scuff on inside near where spur meets pinion. Runs completely free otherwise.
2. Old black - Good sized worn area where larger portion of spur gear caught up. Same spot. See photo below.
3. New black - Installed spur gear and found it got jammed on the same spot.
So, yeah, there's a minor problem, but as pointed out on rc-mini.net years ago With all the gears in, put the 2 chassis halves together (Just rubber band them together) and then put an outdrive in each side of the diff. Now spin the transmission using the outdrives. You need to listen for any sounds of the gears scraping internally.
That was written when the white gears were the only ones available. Just hit the offending spot with a Dremel and you're golden.
I did also notice the gear mesh was a little tighter using the black gears using both Tamiya and Robinson Racing pinions. A little sanding on the outer edge of the spur could easily resolve this.
So, there you go.