Welcome !! As an Owner of a '89 XJ600 Paperweight I was interested in all you went through. Mine will hopefully be getting worked on this winter when I get my new "Man Cave" !! ( Ordered & awaiting delivery 6-8 weeks) Also having previously owned a Pre Divi XJ600 I can remember it having a "Buzz" around the 4-6000rpm so I think that it may be part of the character of these particular bikes.