I've heard the engine was mounted a bit high in them and affected handling. David makes an important point about the maintenance - I knew I was getting a Pantera, but I still looked at some other cars during my research to get a sense for where pricing was headed, and Ferrari maintenance costs came up a lot as an issue.
I'd had some comments on the aesthetics of the 512, but that's a personal opinion and I don't think would really help you in your decision ... so I'll stick with what I think is the best thing you can do before jumping into such a purchase.
Based on my experience with researching and buying the Pantera - I'd highly recommend you take time to read the community blogs - I initially read reviews that highlighted the challenges of the Pantera, but after reading the blogs/forums, I found that there was a community of passionate owners who not only talked about how they updated their cars, but were actively helping each other and no problem is too minor, if someone knows the answer, they post it. If the Ferrari 512BB crowd isn't the same, I think you'd be disappointed in the long run.
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