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 one to die, loses."
2013 Triumph Thuxton, from my friend, the late Randy Lusk
2010 R1200 GS Adventure 30th Anniversary Edition with cool paint job
2006 R1200 GS Adventure (with 3 very expensive bags and ABS) (Gone to motorcycle heaven)
2002 R1100 SBX