Hey Ragged, it may *not* be the clutch. It can take many oil changes to get rid of the crap off the clutch.
Was the clutch working perfectly prior to using the car oil? If so, I'd reckon that it's the car oil that did it.
I think that you have two choices:
1. Buy a LOT of cheap 10/40 motorcycle oil and change it out after a hard run about 3 times to see if there's an improvement. Keep the filter (after emptying it), change the oil.
2. Pull the clutch (potentially the most expensive route) and replace.
3. The lesson you'll have learned is not, not get involved with a Triumph, it's don't use friction modified car oil in a motorcycle with a wet clutch. It's not like no one has ever said that before...
Linz