I took mine to Baxters because of what felt like the clutch slipping in 2nd gear. After Gus test rode it, Toystoretom who was with me, noticed oil on the back side of the head. Gus called Triumph, they Ok'd to tear it down for the upgrade kit and head gasket replacement. Gus then found that the tortional dampner was bad. Everything repaired and upgrade kit installed, all paid for by Triumph, 18 months out of warranty. No questions asked. Guaranted that HD or any of the Jap companies would not of done that. Look what BMW has done to their loyal riders with final drive failures.
It doesn't surprise me that Triumph denies knowledge of the upgrade kit. It probably cost them a lot of money to do that. I remember Gus saying that I couldn't take any pics of the parts to post here.
If you take it anywhere I would give Gus first shot. I think he has a good relationship with Triumph and he has tore into dozens of them. That is something especially to consider if you are paying for someone's time. At minium he would be able to tell what the problem is from riding it and could make a case for you to Triumph.