Don,
After being on this list for the last ten+ years, I would not say that ECUs
are a high failure item. I do know they develop fatigue cracks at the solder
joints of a couple large components. This however does not cause total
system failure. Instead you experience a momentary hiccup. I just re-flowed
the solder joints, a fifteen minute, easy fix.
   On the other hand, I have been meaning to buy a spare. Just not a high
priority for the above reasons. 266k miles on this one so far.
  The 928 sounds like a good candidate for a small block Chevy engine with
carbs.
Ken Lewis
http://neksiwel.20m.com/