Well, a little science experiment today. I pulled the gearbox and disassembled to remove the offending gear. It's a composite piece, the brass gear has a hollow extension that the bevel gear is mounted on. I came up with 3 ways to fix the issue.
Number one was to drill several very small holes parallel to the bore axis. I'd then insert steel rod into the holes to lock the two gears together. Possible to do, but it would require a good drill press, steady hands, and there's the chance that the wire would shear under load. Plus it was hard so I put it in the possible pile.
Number two was to wick some bushing locker between the two pieces. I cleaned it very well with carb cleaner and soaked it in some alcohol to ensure that I got any oil out of the space between the two gears. That was a requirement for any method I used, so... I had the sleeve locker, problem is it's pretty viscous and wouldn't wick into the gap, at least I didn't think it would. I also thought ab out doing the same thing with thin CA. Not a bad thought, worse case is it fails and I have to do it again. But...
Number three. I take an approproiatley sized center punch, put the taper in the bore, and tap away. It might spread the brass enough that the other gear got locked back into place. Table that one for a minute as well, as I don't have a big enough punch anyway.
Number four.... there was solder on the brass gear, an attempt I guess to lock the two together with solder. NOt a bad idea... and I got my little torch out to try and remove the solder from the brass gear, I thought why not just try and wick some solder between the gears and braze them together.
Well.
I heated it up and got some of the solder off. I let it cool off and saw a few blobs between teeth so I broke the torch out again. However, while heating it up, I discovered that the melting point of the metal Tamiya used to make the bevel gear is somewhat lower than the temperature that solder reliably melts at.
Yep. I melted the gear. I noticed it looked "shiny" while heating, and I tapped the whole gear on the table to see if the solder was ready to fall off. Much to my surprise, the entire bevel gear turned into a molten blob of metal and fell on the table.
Whoops.
Anyway, I note that particular gear seems to be the same in every single Tamiya double clutch gearbox. I'll pull the Gepard out and verify, as I don't think I'm going to keep the dual clutch setup in it when I get around to it. I did win a bid on a Tamiya Sherman on Ebay, with that style gearbox, for a low enough price that I'm willing to part it out. So hopefully salvation is at hand.
And on a completly different note, I started disassembling the KT. I wasn't gonna do it, but noted that 80% of the road wheels were frozen in place, as were 50% of the idlers. So, might as well. I love the guy that put this tank together. He used was very generous with the locktite. And not blue, either. Or it might be the Tamiya stuff, I'm not sure. Anyway.
Hello, if I understand correctly? the bevel pinion is detached from the brass one? Is it not possible to pierce the cylindrical part of the cone, and cross the axis, to insert a metal rod (pin) or tip turned on one side.
That's what I'm going to use to motorize my "static" KT kit. 
