By Almighty

The actual work of takedown, replacement of parts and reassembly.. takes only less than 20 minutes. I figure the gun/or AEG unit would spend more time travelling if sent to the dealer.

This is the inside of the AEG. The arrows point to where the bushings are placed.

Here are the bushings, shown almost full size - these are the metal replacements already.

Make sure the piston is in rest position by checking if feed nozzle is forward. If not, fire gun several times until nozzle is forward.
To open AEG unit:

Lay AEG flat on table facing right. Remove all screws, and then slowly pry top half off all around - keeping cylinder down with your right index finger. This will keep the spring from buckling and popping everything out.

Ease the (rear) spring guide out so as to relax the spring, and then fully open the AEG.
To close AEG unit:

Compress the spring and put into its proper position, pressing down on it and the cylinder to keep it from buckling. This is best done with the right index or middle finger through the opening of the upper half of the AEG housing.

Slowly close the AEG halves together and align the gear arxles with their respective holes.

Almighty beat me by a few minutes, but I might as well post this anyway (nice pics, btw!)

I bought a non-working MP5, and since I couldn't do any harm, I tore the whole thing apart, including the gearbox. It was really quite straightforward; arrange the screws and parts in a logical sequence so you put them back in the proper spots (some have different threads and lengths).

When cracking open the gearbox, once the initial spray of parts subsides (from the mainspring releasing; it's really not *that* bad =), pull the halves apart. Three reduction gears are there, and the last two seemed awfully "grind-prone" to me, so I stuck an extra washer under one of them to reduce the "overlap" a bit.

Don't forget to clean all the black crap off the trigger contacts while you've got it open!

The two NON-obvious things when reassembling: make sure the plastic nipple thingy (which slides back to let a BB in) is positioned properly, and check the little ratcheting lever on the first reduction gear; you wouldn't want that thing to be out of place or it'll chew up the motor's sprocket.

Oh yeah, if you're curious: I did actually get the thing working.

I wouldn't recommend it to just anybody, but if you've assembled RC cars, this is a really simple do-it-yourself job. MINI airsofts, on the other hand, are a can of worms; I may NEVER get my mini-M16 put back together =(