Oil - what to do?
 

Driving home, the oil warning light came on during a long slow down at idle (coasting up to lights) and then went out again. I assume the oil pickup is at the rear and there was a little starvation, but it must be pretty low which is a bit of a worry. So I need advice; do I

a) Drive to the nearest garage and fill up with half-decent 5-W30?
b) Sling in the pint of 10-W10 that I have in the garage and then go get some more 10-W40 to top up?
c) Sling in the pint of 10-W10 that I have in the garage and then go get some decent 5-W30 to top up? (and is mixing grades really all that bad)

What's best?

Two supplementary questions,

Does oil "go off" if it's just stored, i.e. does it have a shelf life?
What grade of oil would the Subaru delaers use at a service (it's a MY03 WRX) as I can't check as I don't have the paperwork?

Sorry if this is all a bit dull, but I thought I'd ask before I go and fill my lubrication system up with ****e that'll sieze the bearings before you can blink.

The answer is c)

Low oil level is far, far worse than anything you would chuck in to bring the level up

yeah something is better than nothing..