The knuckle is the prop shaft universal, Valdas or HealyC maybe able to confirm but in pretty sure the universal is replaceable on it's own.

Listermint is bang on about the support bearing, it could be a combination of both.

I wouldn't just throw money at the thing, it's easy to throw thousands at an e39 and get nowhere. You would be much better off taking it to someone who knows them, long run it'll be cheaper.