I think the leather is standard, just no one has ever sat on it! In comparison, the leather in my 128k M5 has the texture of an elephant's testicle (not that I've ever felt one)
this M5 has a non original full leather interior, with the seats sewn as a highline 6 or a M5 e34.
What a shame.
Even the rest is aftermarket and clearly not BMW.
My concern would be whether the mileage is genuine. They can easily hide the interior wear and tear with new interior and carpets. I would pay a premium for a low mileage car. Am looking at 52,000km #179 right now.
We need steve's careful eye to check out the originality - I would say dash and doors are standard trim, seats and area around the gearstick are reupholstered, but noticed the tyres are likely not original Michelin - not sure but one of the wheels seems to have the factory original chrome covered wheel weights...