B&W has a great reputation for support and making diagrams available. I would take your questions over to the multi way speaker forum at diyaudio where youll get knowledgeable help troubleshooting and fixing them.
gearyb... where do you live? I also doubt that it is the crossover. If needed, can you pull both crossovers. In your circumstance, I would give you the labor to repair these at N/C, you'll need to supply shipping and parts. I would need both crossovers to keep matched pairs on any parts changes to ensure matched sound quality.....
But again, I doubt that it is the crossover.
1st. reverse the speaker cables from the left and right speakers and make sure that you don't have a channel out in the amp. If the amp is good, then:
1) is the entire speaker dead?
2) if not, which driver is not working?
3) If the whole speaker is dead, I would recommend that you access, 1 individual speaker and touch your speaker cable to the single driver... i.e bass, mid or tweeter and play it at very low volume. If the individual speaker plays and your amp does not have a channel out, then yes, we are heading toward a bad crossover.
All of this needs to be checked before we go any further.