Massively problematic.

DO NOT be lulled into a false sense of trust by your prior BWM, even V8 BMW, experiences. (I have a E39M5 with 225k.)

You are buying one of the weakest BMW v8s, with serious lubrication failures early in their lives, and on top of this questionable history you are also seeking 'mods'.. (like what? What mods are there for X5Ms, other than eye candy, maybe a muffler).

Luckily, you are rich- so it should only be an annoyance- not real pain.

(kidding)