Here is the info on that.
Older Rockets were to use Mobil 1 15W/50 made in Europe. Since then Triumph ended their relationship with Mobil 1 and changed over to Castrol. Now they use the Castrol Full Synthetic 4T 10W/50. According to the Triumph Global Marketing guy Nick I met at the Bonneville Salt Flats during the Streamliners last attempt in September. Castrol is not sponsoring the streamliner because it has been 3 years and they haven't been able to produce the desired results.
Nick is on the right. He gave Jerry and I each a Pit Crew shirt.