I blasted through about 400 rounds with mine on a Saturday, pulled it apart for cleaning the next day and was horrified to see rust already forming on the gas piston and inner gas tube. Now I carry a bottle of Windex with me to the range (even plain water will do) to flush the gas system just before I pack it in for the day.
On another note, a buddy of mine gave me his ChiCom SKS to fix that he fired a bunch of corrosive ammo through, and then "threw it under his bed and forgot about it" for a few years. Wow, what a freakin' mess-the gas cylinder had become one with the gas tube-totally siezed, and the bolt/carrier assembly was rusty too. Took me a couple of days to loosen everything up, but the inner surface of the gas tube was totally scored,
I think he has a nice bolt action SKS now....