At least it’s a proper Triumph now
The word on the Internet is that it’s probably the oil filter. I’ve given it, and the sump plug, an eighth of a turn with no effect.
The plan is to get to Walmart for a top up, then Denver for a new filter (Triumph, this time, not pattern) then another Walmart for more oil and a catch tray, then a secluded bit of campsite somewhere to do the work.