I actually bought the upgrade kit from Losi for my micro D/T. It included the 27 Mhz RX and servo with servo saver. It ran me about $30 as I remember. It's been more than a couple of days so I'm not sure.....
As for metal gears, you don't really need them. I run 10250kv brushless and 2s LiPo and haven't had a single problem with the plastic gears onthe servo after 6-months.