I still have the problem. I had the bike back to the dealer and they can't find anything wrong. They have been more than accommodating, removed the primary, clutch basket, inspected the bearings, etc. 9,000 more miles and no improvement. I would think if it was a bearing or other mechanical issue it would get worse, but it hasn't. Right side still solid as a rock.
I I checked and double checked all the exhaust clamps, have even replaced the exhaust since then and still the problem exists, and still only on the left side.
I took the rear floorboards off my Road King Classic, which she loves to ride on the back of. and swapped them with the ones on the SEUC. They seemed to have much better vibration isolation than the fancy, much better looking SEUC ones. Took a ride, a while it was a little better, it was still unbearable after a while.
Still frustrated. I'm kind of hoping the flywheel shifts on me soon. Maybe it's out of spec on the primary side. But then again, I think I would feel the vibration if that were the case.