can you describe the fault in more detail.
is the engine misfiring or does it just fail to turn over on the starter from time to time?
ECU = difficult - can be removed and sent off for repair (try ecudoctor.co.uk)
Black box controlling power circuit to starter motor = remove, prise open, locate corroded part of circuit board using Mk1 eyeball and test meter, bridge out faulty section with soldering iron and wire, close up, test on car, reseal with silicone if ok.
worked for me on a 1.3i rover lump and saved me £100