The 3.0lt is the T6 like my V60 and it is a hoot to drive that motor , turbo six , there is 3.2lt six non turbo but slower and thirsty , the T6 a bit thirsty but ohh the power!
The aforementioned Haldex is rear differential and has a bearing that fails , needs fixed with a Land Rover brand bearing or some joints machine out the seat and put larger one in, the big rubber bush on diff went on mine and the lads at Berry Motor Group said that was uncommon.
Having fluid flush/dump and fill on gearbox is a must to ensure it lasts, done regularly , say 40K KLM afterwards plus the Haldex fluid and filter too. This servicing isn't done at dealer so tell us where you are and someone will advise on a great Indie Volvo shop. Gearbox and diff applies to Diesel and T6.
The smaller diesel can have a rubbish gearbox , I'm unfamiliar with your initial choice model though.
A higher mileage T6 may or may not use oil, it's a T6 thing, mine got worse now after 200K KLM.
Les