The Crank angle sensor is in the distributor, so 4 way connector going to the distributor should be checked.
Has it already had a new distributor if the sensor has been replaced, or has it actually had a new CYL sensor (behind the cam sprocket, as that has a habit of melting)
If the distributor has not been replaced, then check that as failing bearing inside can cause its freeplay to damage the sensors.
Both the TDC and Crank Angle sensors resistance can be checked (should be between 800 - 1300 ohms), it is presumably breaking down when hot.
Otherwise as you have eliminated the ECU, then wiring from engine back to ECU would be next to check.
Steve M
__________________
Its all gone Norfolk!!!
Now in the Lotus position.