Just a guess, input shaft bearing. Had exactly the same type of description as what you gave and that's what they found on pulling it apart. It felt just a shade unsmooth until you pushed on it at the same time as turning it, then it was downright gritty. Be interesting to hear how it turns out.
Let's settle this the old-fashioned Navy way, first guy to die; loses.
2014 F800 GSA, 2010 R1200 GSA, 2013 Triumph Thuxton, from my friend, Randy Lusk
USMC, Motor Officer, SF... Been there, done that, got the t-shirt, then got too fat to wear it. :(
Motorcycled Prudhoe Bay to Key West, no room for a t-shirt on that 13,500 mile odyssey.