I hear you about the Austin-Healey 3000, wouldn't mind one myself as I've always liked those cars but have never driven one.

I can't tell you what code reader you need as I too work in a dealer so only use Volvos VST for '96-'98 cars. I'd think that someone here might know however.

If you went into the dealer with flashing LEDs, still had flashing LEDs with a new control unit (panel), they did NOT diagnose a bad ECC unit correctly as the real problem still exists and at that time, they should have re-installed your original unit. In reality, ECC units almost never fail (VERY rare). There is NO fault tracing for an ECC unit, just all the connecting sensors and flashing LEDs indicate a sensor or motor problem.
Have you tryed talking nicely to their service manager or general manager? They really should resolve that for you at their expence now that they've mis-daignosed your problem and I know that ECC units aren't exactly cheap either.