Being viscous is bad (ie. Honey has a high viscosity). You want something "non viscous" or as non viscous as possible (such as water or liquid nitrogen).
RC Hobby shops sell 100% pure silicone oil as RC Shock Fluid. 20 wt. is less is what you want. Preferably 10 wt. or less. Airsoft Innovations' silicone oil is 1.5 wt. from what I have read and is the lightest commercially available (usually this is for industrial uses and you must order large amounts of it).
ಠ_ಠLess QQ more Pew Pew
READY TO >> RACE