The B58 and 8 speed ZF is/was also used in the BMW '40' saloon and coupe models, some 35s too and the X5 and X7. But with a variety of different tuning. Probably tens of thousands built, with a very good reliability record, if looked after.
So, it's the bespoke Morgan bits that are exclusively P6 I expect will become more difficult. That includes the engine parts adapted to the P6 by Morgan, such as the cooling system. I also expect some of these will be the parts of the car more likely to require attention over time!
Nothing I can do, I'm happy enough to roll with it. I was just surprised how few may have been built, making the problem more likely.