Which Oil to use P38 4.0se & what is that hole for?????

Hi all
i have a P38 4.0SE only had it a few months oil has got a little low

Any advice as to what oil i should use. You guys will know the best. i have no idea what was in it before.
Any help would be good as i am doing a 400 mile trip this weekend

Also does anyone know what the orifice below the clock is for????????

Cheers all in advance
Carl

Look in the cars handbook for oil specs,I would change it if you dont know when it was last done. The little hole has a fan inside it to suck air in to monitor cabin temp.