Happened my 520i, was Silver and when it came to the end the back would be covered in black around the exhaust, anytime I polished the exhaust it was black after short time.

Think it turned out to be valve stems, I done all the above gaskets and it actually got worse, presume it was because more pressure on the actually stems?

Some of the gaskets are cheap so do them while your doing the CCV.

Take it to Valdas he has had a fair few e39's himself.