i think the major part is the mags...I know for gas mags, just put some green gas in there..as knight already said. I use propane + silicone at the field, but I use greengas to store it. What I do is usually shoot the propane all out using my spare bbs. Then add like a second of green gas..although leaving propane + silicone is the same thing..But I like to do it the sure way.
CO2 mags..just make sure you don't leave the co2 in the mag before storing it..get rid of it. Other than that its all in the post above..and I'm pretty sure there is a sticky somewhere about GBB maintenance .