E70 4.8 is not for the faint of heart. We love driving ours, but don't always love owning it.

Things that pretty much every car needs replaced at some point:

Upper timing cover gasket (both sides)
Valve cover gaskets (both sides)
Alternator bracket gasket
Valley pan gasket
Coolant transfer pipe
Air springs

In addition, some cars need valve seals replaced, and some experience rear differential failure.

We bought our 2008 X5 4.8 in 2011 with 38k miles. It now has 95k and has experienced all of the above except valve seals.

If your friend isn't willing / able to do his own work these things can get outrageously expensive.