Does anyone know what would cause damage to the carbon brush within the dist. cap? Mine looks like it scorched. Replaced and slightly scorched looking again. What causes this....a dodgy coil perhaps?

I am not so good on the electrics side but I guess it could be spark errosion for some reason. I have just been through some frustrating ignition problems myself and while I was at it I sorted out all of my 126 distributors and rebuilt the good ones. I found that the rotor arms when worn will rock about which could cause wear. I found that if the carbon brush was sticking then there was poor contact with the rotor arm. Then if the spring clips are faulty then the distributor cap will vibrate and if left will wear away the locating part on the distributor main body.

Excess movement somewhere will be causing this. The coil etc will not affect it.

Look at cap. Wear/ burning away of the hole the pin fits in. Loose cap.

The main shaft of the distributor itself. Try pushing it side to side to check for wear. Note that wear here will be affecting your points adversely too.