I recently made the switch to castrol in the daily, it's a cheap oil with decent additives.
Apparently t6 has changed their formula a few times in the last decade.
May 2017 VOA: https://bobistheoilguy.com/forums/threads/voa-shell-rotella-t6-may-2017.270486/#post-4408001
July 2011 VOA: https://bobistheoilguy.com/forums/threads/shell-rotella-t6-5w40-voa.158546/#post-2330040