Well, I question old mate's diagnostic technique.
He says:
now by 'dropped pressure' I would assume that means no compression? But how he tells it has no compression in 1 cylinder without testing them I don't know, and if he'd tested them he'd know which one it is. If its actually got no compression on 1 cylinder, forget it, its f**ked.
IF he actually means "not firing" on 1 cylinder then it could be something simple causing no fuel or spark to that cylinder, in which case it would probably be a very easy fix.
I would suggest, if you have any intention on buying it, do a compression test on it first and if the cylinders aren't all in spec and fairly even, then stay far FAR away, it's not worth the hassle.