what is a good servo I can get from hobbyking that will be a direct fit in the Caldera 10e?
Something like a Savox SC-1258TG
would be perfect and would last you forever, however for less money I've also had great luck with the EXI D226F
from HobbyPartz (though you'll need a 23t servo horn). I haven't bought a HobbyKing servo yet, but I've heard of many others using their BlueBird line: look for something digital and metal-gear closer to 0.10s and 10kg/cm, like this one: BMS-825DMG+HS
also, might you know the part number of the screw that goes into the bottom of the hub in the front that holds the hub in. hard to explain.
I know exactly the screw you mean: it falls out for everyone
Those screws and their little metal sleeves come with the plastic hubs, but they fall out so often you'll be less frustrated and end up saving money with a more permanent fix. If you switch to the metal hubs from the 1/8th-1/6th Redcats not only do you get the stronger hub you also get larger M4 screws as well... and they can be threadlocked since you're screwing them into metal. After making the switch, mine have never fallen out again.
You'll need three parts from HobbyKing: the metal steering hubs
that accept the larger screws, and the C-hub's they screw into
(and other side
): about $15+shipping. The Redcat part numbers are BS903-111
("N" is the important part for the larger holes, this number covers both C-hubs) - but I would shop around Redcat resellers, since they charge more than HobbyKing.