Do not use silicon oil. If the oil reaches the glowplug, it will be an insulator for the heat from the plugfilament, and your ngine wont run right before you change your glowplug.
Audi, VW amongst other says do not use silicon liquid gaskets as the residue or fumes can damage airmass meters, oksygen and tempsensors. Use bearing oil or spit.
There are two types of silicon gasket, the old type releases acetic acid when drying, the new RTV silicon is sensor safe.
I for one use RTV silicon to fill my cranks...
I also use silicon oil from time to time to lubricate the gaskets, you don't need much.
If I remember correctly silicone oil is inert also.