Well, if the ECU has been swapped out, and the brake switch looks "iffy" that's a cheap thing to change (but I thought it was more to do with the Cruise/Control than ABS).
The High/Low pressure switch has been known to fail on the ABS. I have seen a few threads on forums about it.
Good Luck!
On my model year there are 2 physical brake switches... One for the cruise control which has a 2 pin connection but also has a physical vacuum line attached to it to vent excess cruise control pressure. This is higher up on the pedal.
And then the second one which seems to be the same switch fitted to freelander, discovery, etc.. and has 3 pins with two internal switches for redundancy.
I've actually already replaced the 'top' cruise control brake switch as someone had busted the clips, so may as well replace the bottom one now.
Thanks for the tip of looking at the pressure switch... I'll take a look into that