It turns out that the azimuth was way off. I was able to use a mono tape to bring the adjustment back. Thank you Dillen for giving me the idea. 😁 Once the azimuth is reasonably close the factory tape works fine. Now the question is, what would cause such a drastic change? Did something break or perhaps the last time service was performed the transport wasn't assembled correctly?

All tape and especially Type II (Chome) will lose a couple of dB in strength over the years as the oxides weaken over time 🙂

Also, rough transport and many plays can wegde azimuth out of adjustment.

If the azimuth seems to be WAAY out on one of these "wedge-shaped" cassette machines, it's usually caused by a crack(s) in the plastic molding(s) on the mechanism that holds the springs(s) that keep the head-block in place as it moves back and forth.  The little clip that holds the cassette in place when it plays sometimes keeps things working okay, but it's not consistent, especially among different tapes.

BC9000 is a wonderful deck when it works correctly; keep in mind that it may need a comprehensive service if this has never been done before.

My complete Beosystem 8000 is due for major service, I just been feeling like a kid on Christmas Day since I opened the boxes, which for the most part had been in storage since 1988. Of course I tell everyone that I need to discover exactly what the problems are so I can pass this vital information on to the service people.

When I made the initial azimuth adjustment, the mono tape and B&O's alignment tape didn't exactly agree so I settle on something pretty close to midway. This was close enough to get the deck working quite well, playback seemed fine and my test recording revealed no audible crosstalk. Since then I have relied exclusively on the B&O tape to tweak the azimuth adjustment twice, now the deck really sounds fantastic, but I have only been playing with one tape. I intend to keep checking the azimuth and normally I use a variety of tapes so if the plastic is broken I’ll definitely want to get it fixed.

How hard is it to get parts and do you have any idea as to cost?

Try adjusting the azimuth and then setting the screw with some nail varnish, just be careful that it only goes on the screw tho!

Regards spares for this deck your only hope for most of it would be to purchase a spare deck and butcher for parts. They are extremely cheap atm, and considering what other tape machines can fetch and this machines historical importance to the tape market (first deck to ever feature HXpro and surely amongst the first to feature Dolby C???) I think they are currently undervalued to some extent!