thanks to the forum for  information.
I used a 10 mm tube as a guide and a long 9 mm drill to drill  the snapped of end of the long bolt[approx 120 mm] on the chain side that always snaps.
the small piece that was broken fell down to the workshop floor when i put the new bolt in ,  it was about 5 mm long
i sprayed lots of lubricant a few days before and used cutting fluid on the drill.