It won't start because:
1. it doesn't crank?
2. it cranks but won't fire?
3. have you checked the glow plug relay's fuse?
Oil inside the air cleaner is common and can be fixed so don't let that
mislead you as to the current no start problem.
These engines don't just die, they exhibit lots of symptoms before their
death so take another look at it.
Glow plug relay is a black box on the left fender. It has a plastic
cover that unlatches and slides UP. Under that cover is an 80 amp fuse
or fusible link; it should be intact, your car's is probably not and
needs to be replaced. Dealer sells these for $1 or $2, buy a spare.