I would agree with the statement that they are not rare; although you don't find them on every streetcorner either.
As with the other M117 engines, timing chain guide failure is a distinct possibility with this car as well. One moment you're happy-go-lucky, the next, you're looking at $4k in repairs.
What I am trying to say is: Better make sure the rails have been recently replaced. If not, beat the guy up on his price, and get them replaced after you've bought it - because guide failure is no where near as rare as an SEC.
PS: I thought I heard somewhere that used car dealers will tell you whatever they need to, to get top dollar for their car

But that could just be a vicious rumor