Engine oil Castrol or AMSOIL

I put 5w40 in mine, that's what is recommended for mk6 at all temps. Summer or winter months. I use Castrol Edge Full Synthetic high mileage, works a charm.

I run Amsoil 5w40 warmer temps and Ravenol 5w30 colder temps.

The 0-20 Castrol VW Spec oil I buy from my dealer is cheaper than any 0-20 from Walmart or auto parts stores. My 2019 GSW has 16,000 miles and uses next to no oil between changes. I have averaged over 40 mpg for the 16K miles.

Stage 2+ 2016 wrx here, in my experience (with having run both full synthetic amzoil and motul) I can honestly say that while both are rated very good for the FA-20 I would lean toward the motul simply for responsiveness. The car just seems to respond better to that brand, 100% just off personal experience

When it comes to oil I have one thing to say. Use Valvoline or Castrol 3000 for conventional 5 to 7000 for synthetic,. If you do this and take good care of your vehicle your car will go 200,000 to 300,000 miles.

I happen to use Castrol in all my gasoline powered vehicles and have had no oil related issues. Given that VW promoted Castrol and, more importantly, that I prefer Castrol in general, I’m staying with Castrol when I can... I've had no oil loss in the Tig with Castrol and see no reason to switch to a different brand just because some MBAhole behind a desk made a profit driven decision to switch suppliers.

I use 15w40 GTX Diesel Castrol oil, it works.

My 10k UOAs on Castrol 5w40 were just fine, but VW 504 is mid-saps so it might not have as much staying power even thought it's "better" oil.

Our Tig is coming up on it's 4th change (every 5K) and hasn't lost any significant amount between changes. So far all changes have been the 508 spec Castrol 0w20.

You can't go wrong with the Amsoil XL. I run OE 5w30, which offers plenty of protection for a stock engine. Unless your tolerances and clearances have changed, there is no reason you need 5w40. Modern synthetics, especially ones designed for the extra heat of a turbo, are outstanding oils.