Magneto Condenser

[Charles P]

My car is suffering and the finger of suspicion is pointing at the ML RF4 magneto. 
It's misfiring when hot and seems very down on power, again when hot. Earlier today it stopped sparking altogether for a while when hot. 
It was fully rebuilt a decade ago by the late Tony Holder, so the coils are properly wound modern ones, also being a rotating magnet type, the coils have an easier time. 
My thought is that the condenser (capacitor) is failing. 
Two questions: 
1/ What are the signs of a failing condenser?
2/ Has anyone found a suitable replacement for an ML mag?

Thanks

Charles