Erik, I support your verdict about fancy caps in magnetos. Like you I cannot see how these cool caps can handle high AC voltage from magneto applications, the size is just too small. Allright, with very poor - ahmm Lucas magnetos - they may have no short time problem but we want fat sparks from decent coils , so then there will be substantial AC spikes in a coil-capacitor circuit.
MM has not tested WIMA caps but that does not mean they would not be up to the job. The MKP10 series is just the best type I believe and WIMA do them for 50 years , so they know their business - and their products are locally produced all that time and no imports from Asia. So I put my faith into these for reliable specifications.
There seem to be lots of reports about poor performances from modern typical capacitors made for classics, bike or car, so I will replace most of them for the MKP10 types, as I can see specifications printed on them - unlike classics which just say Bosch 0.22myF at best.
Vic
P.S. I do tests in the oven at 70 degrees C and 5 hours for checking performance at higher temperatures. No great idea just to spin the mag by hand for sparks while in cold state.