Building a G3R need some help!

[Race495]

http://cgi.ebay.com/Traxxas-E-Maxx-G...3A2%7C294%3A50

Here is the stock case, the only issue with buying a whole 3906 tranny on ebay is you don't know what the internals look like and they usually go for around $30-40 on there so there is no big savings. Are you planning on doing the Revo slipper/input shaft in this tranny? If so then there is even more reason not to buy a whole setup.

You figure the only pieces you will use from a stock tranny (prices are approx):
1) output shaft $10
2) case $10
3) 2nd gear $5
4) Motor mount $15

So why buy an unknown used one (unless you can get it for $20-25 shipped when you can have all NEW parts for a little more?