"They refuse to play properly".
What does that mean?
NO SOUND at all?
Only some individual drivers are making sound?
Crossover issues like broken solder joints, maybe bad capacitors. I think there is a mid range adjustment l-pad that might need cleaning, those do go bad.
Check the fuse holders for clamping pressure on the ends of the fuse, if they are a little loose the fuse may lose contact on one end or the other.
The Walsh "ice cream cone" super tweeters do go bad as well, might want to check them with a multi meter, Check the Walsh foam as well just to make sure it is present and what condition it is in.
That ought to get you started.