If you plan on getting an old, used BMW(and E39s are old and many are VERY used), it should NOT be your one and only car. Have a 2nd spare car.
My E39 is a 1996 model, and I've had it since 2008.So far, it has served me well.But based on my previous experience with BMWs, I know my baby has a surprise waiting for me just around the corner.Its not a question of IF, but WHEN. When that happens, I have my 1995 Audi A6(C4) to drive as a backup car.Had the Audi since 2005, and the only failure was a broken passenger side power window switch.I can thrash the Audi within an inch of its life and it will still keep going, but its also no fun to drive.
With so many complaints about BMW's reliability in this forum and from around the world, it just boggles my mind how BMW managed to become the top selling luxury brand in the world.