silicone oil shouldn't really be used for slide lubrication. White Lithium grease is great for gbb slides, or any other machine oil that is not too thick.
Silicone however, should be used for o-rings, and the hopup rubber once every while so that it doesn't become too dry. Using silicone on orings such as the main one on the piston of ur gbb, makes for a good seal. Another good thing about silicone (light silicone) oil is that if your oring should decrease in size because of cold (I had a gbb and aeg orings decrease since I stored them in my basement were it is pretty cold) you can take the orings, soak them in the oil for a day or so, and they swell, providing for a good seal.
Get light silicone oil.
Ive used this before, gets good results: http://www.canadiantire.ca/AST/brows...mbo%2BPack.jsp
OR just buy the AI silicone oil tube, itll last you long if u use it properly.