I'm not sure what part that is in your photo or what kind of retaining bolt was in there.
But this is as good a place as any to mention that several
M59 owners have reported bending backhoe bucket parts because they were using a lynch-pin to retain the main backhoe bucket pivot pin.
A backhoe bucket is clearly the wrong place to have a lynch-pin retaining a pin. Mine did come that way but I quickly replaced it. You should use a more positive fastener at the backhoe bucket.
rScotty
photo of a lynch-pin or linch pin