Rotor arm of the moulded in strip variety & not the riveted on strip type?
This style: Lucas 35D V8 Rotor Arm Red with Powermax Technology (simonbbc.com)
Not this type: MGB V8 ROTOR ARM GRA2133 (mgbhive.co.uk)
Although I'd be inclined to think you'd have a misfire all the time if it was faulty...