Hi guys, need a bit of help please.

Looking at buying a 1998 VT commodore for one of my lads, the car seems in great condition but has high km's (300,000)

The problem is its only firing on 4 cylinders, there is no spark from the passenger side coil (1+4 ?) for either of the associated plugs.
The guy who is selling says he has replaced the coil, plugs and leads.
I was thinking maybe the DFI or CAS?
He seems to think there is a problem with the CAS, would this effect just one coil or if it was stuffed would it effect all the coils?

Any ideas would be much appreciated.

Cheers