is there a way to repair this??

there's AUGs for sale at a website with stripped piston heads and I want to know if I could buy one and fix it.

I think you could just buy a new piston head or even a new piston.....someone correct me if I'm wrong.

and if he's right how much would this cost?

i think that a striped piston means that the teeth were striped and i think this may be the part you are looking for but it is hart to tell with out seeing the site...
you should post the site...and ask other people what they think because i may be wrong.
http://www.airsoftpost.com/matrix-high-speed-full-teeth-piston-metal-teeth-strip-airsoft-gearbox-p-30044.html

the problem is the site is wierd because it works was one page essentialy. so you have to go to www.shortyusa.com and look ok the second page of the 'specails' section. any help wout be greatly apreciated.

on futher reasurch I found that it will mor be easy but will be cheap. thanx for the help

A stripped piston head ???

It has to be a stripped piston,

If you are familiar with GB dis-assembly, no problem, depending on the price of the gun, you could be saving yourself a good load of money.

First find out what kind of Piston was installed, if it was a Plastic or Full POM piston, O.K., if it was a piston with Metal Teeth, go for a big reduction in the Price, chances are the gears are also damaged, could be that they are ok 50/50 chance.

well it's a factory default

well if it is a factory installed piston, then it is most likly POM or Plastic, The sector gear shaved its way through the piston, little to worry about, except for cleaning all the junk out of the GB.