The cruise control uses inputs from both the clutch and brake pedal sensors. The symptom you describe; cruise deactivated until restart, is the normal reaction to a sensor input fault. Any more than five inputs that don't make sense and it deactivates.
This is usually the brake pedal sensor which has an internal adjuster for wear. You can pull this apart easily enough and reset it btw - or replace it if faulty but make sure it goes back correctly, if the length is too long it will flicker, sending false inputs to the ECU.
One easy way to identify this when your driving is to see if your brake lights are flickering on and off, when your not using them (obviously). You can do this by removing one brake lamp, going for a drive and seeing if the bulb blown indicator flashes on and off intermittently. Or have somebody follow you.
Also, check that the brake pedal sensor fitted is the correct type, there are two I believe.
Check the clutch sensor too, it may also be loose and flickering (in the mind of the ECU)
I doubt you need a new ECU for all the reasons you list, incl. the fact that it is supposed to disable the cruise until restart when there is a fault!
03 1.9JTD8v Sportwagon +GTA teledials for the win!!
Last edited by craig_m67; 19-12-13 at 10:36.