what gun do you have?
what crapped out?
whats your budget?
if you have a good or ok gear box then:::
call airdog
get internals (trust me they have the good stuff at a great price.it is hanging on the wall and ready to install)
you may spend a few more $$ with them over the mega all this crap .com ,but the items they sell are proven in the GA airsoft playing fields.
if your gearbox is crap but the internals are good,then get a gearbox.
you may not be able to build your mondo suppa fast hard hitta,but spend your money on good stuff you need and you will be happy
a gear box that can handle 550+ fps on semi can also handle 350 to 400 fps and 30+ rps
i spent alot of cash on crap when i started playing:trust airdog and rhino