Last thing: if you ever needed to change your gearbox's spring, while it's a fairly inexpensive thing to do ($15 or therabouts for a new one), it's a little tricky and can be a bit intimidating to do the first time. There are tutorials here and on youtube. There are a ton of things under spring tension in a gearbox, so be very careful as you open it, or else you'll be greeted by a dozen tiny parts leaping out in graceful arcs before finding some forgotten corner to get lost in. Putting a screwdriver through the spring guide at the rear of the gearbox is the best way to prevent this. Good luck.
@Drake&others: ..and knowing is half the battle! The other half is complaining as your foxhole fills with rain.
Airsoft is where expensive things go to die.