I rarely speculate, when you convert crossovers you look at the parts you want to replace.Pure speculation. These are Japanese caps, neither Bosch nor Siemens. They may be MP, although not very likely, considering the year of manufacture. I have very similarly looking Siemens caps which are polyprops in oil, so we can only hazard guesses what's inside these cans.
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I said check if they don't have their values, replace them. I would replace them immediately.As for MP caps, some of the Siemens MP i have, from the sixties, are among the best sounding caps i have ever come across, especially in the midrange. They have worked for decades at high polarising voltages and still have not developed any significant leakage. Capacitance is also as advertised. At the generally low voltages applied to speaker networks good quality MP caps may last for centuries.
There are already components that I replace without checking them because there are always potential sources of error, e.g. in vintage Japanese amps electrolytic capacitors because they are attached with glue which will permanently degrade the circuit board.Ironically, entire batches of Solen PP from the early nineties turned into dead shorts just sitting pretty on the shelf. I have a few.
My favorite vintage cap Röderstein before Vishay was acquired, where quality was still the priority and not profit maximization was the highest goal








