I had the same thing happen to two studs when I did my 1982 900F. I believe the originals had an interference fit thread on the inserted end and found them impossible to remove with an easy out.
In the end I drilled them out with the tap drill for an M8 Helicoil, re-tapped for an 8mm Heiicoil, used Lock-tite on both the Helicoil insert & the replacement 8mm stud which is available from McMaster-Carr.
McMaster-Carr also has M10 x M8 studs that may work just as well with out the Helicoil insert.
Some machine shops have a electrode-discharge tap and bolt burner & broken tap remover which may work to remove the broken stud leaving the threads somewhat intact...probably still best to install a thread insert.
Mark
