I just ran a fine file carefully around the edge of the brass on my rotor so that the edges were a sharp right angle and any oxidation was removed. Sparks like a nice small sharp edge or point to jump from . Same thing with Spark plugs and the terminals of the distributor cap .
There is nothing much to go wrong with a rotor unless it breaks up into pieces. Its just a bit of plastic and brass.
Make sure you also use a bit of wet n dry on the contact point in the centre ot the rotor where the graphite of the distributor cap presses on the top of the rotor.
Hey Nicola just noticed you have a rather nice Sebring MGBGT Do you race it ? I have had 7x MGB's including a 1962 pull door handle which was the 101th off the line! it wasn't made at Abingdon , the first few hundred cars were made outside until Abingdon had tooled up.
I once telephoned Nobby Hall at the MGB competition dept to ask if a late MGB overdrive gearbox had ever been mated with a early 3 bearing crank gearbox .
He said that it hadn't but should be possible. I made what was possibly the first conversion on one of my cars . It was a lot of work but the 3 bearing crank engine runs a lot freeer than the 5 bearing and is potentially a lot faster. mated with the late gearbox you had the perfect combo.
Love to see a pic of your car