I replaced the cables going to the Knock sensors to no effect, then changed the ECU. The F1 problem went away for about 6 months, then came back on my first leg of my 'round OZ trip. I think I should probably have changed the knock sensors as well, but I havent seen any reports of anyone actually solving the problem for good.
I believe the ECU's are covered in a potting compound, so cant really be repaired. I was going to have a look at fixing my old one, but lent it to someone in this group and they never returned it.