N62 is on the list of BMW engines to avoid. The 4.4L is slightly worse than the 4.8L. Slightly. Reasons?
Oil leaks - lots of them. Main seals, alternator bracket seal, valve cover gaskets, upper timing cover gaskets are common, others come up too.
Valve stems are bad, really bad.
Air pump failure
Intake manifold issues
VANOS issues (like EVERY engine with stupid VANOS)
Coolant transfer pipe - this is an expensive fix.
Plastic timing chain guides that fail.
Aside from those, pay close attention to the entire cooling system. IMPORTANT.
Issues with the air suspension usually the bags. Replacing is only solution.
PITA but not expensive (terribly so, anyway) are the constantly failing door handle carriers.
I know lots about these, as they used to be common around my parts. And a friend bought a used one not too long and he got six months out of it before the cooling system let go and the engine grenaded within seconds. Tread carefully and pay close attention to every little detail.