spent about 1 hour on the phone with Quadral, the manufacturer of those vintage speakers (hand built in 1986 ... whoa ...)
Took out the crossover. While the capacitors still look ok, I cannot tell if they indeed are. Furthermore, the values are not at all what Quadral would want them to be.
They quoted: 130 instead of 70, 47 instead of 56, 1 instead of 4.2, 5.2 instead of 4.2 (all uF).
Now would be a great time to take out the LCR meter and just start checking coils, capacitors and resistors and then adapting the crossover to what they expect it to be.
Which is probably what I am going to do.
*sigh*
If the capacitors turn out to have lost their oompf, it would most likely make sense to replace all of them. After 34 years or so I would expect them to no longer be up to specs.