I had a rear end rebuild on an 09 z last year. And yes yamaha were very expensive for bearings and seals which can be sourced from your local bearing/engineering shop for a fraction, or online/ebay with the numbers.
Here's a bit of info I wrote about the bearing numbers which I obtained from the original parts.
https://www.xt660.com/showthread.php?t=26422

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2011 xt660z.
Yoshimura cans ,kev mod,Dna 2, Stahlkoffer panniers,Hepco Becker box,Givi crash bars,Mita e07 tyres.