Hi Dave, the chain case cover is secured by 2 screws, not bolts; they are just nipped up firmly with a straight edge screwdriver. I can't understand how you broke it off...
Re: the bearing....did you check it for serviceability before you press in back into place...if in doubt...replace it now, as they are cheap and you wont have the bother of trying to get it out if it fails....If it is the original bearing as you say...it will have done a lot of work by now.

They are bolts on mine, not screws. I noticed in Chris' photos that he too has bolts.
I drilled it out and tapped it with M8 tap. Have replaced original bolt with an M8 bolt. All fine now.
I might take the lot down to the mower man and buy a new bearing - He might be able to press it on for me.
My $240 mower is now heading towards price of a new one, but this is more fun.
Blades are now sharp but even following the excellent u-tube demo I can't get it to cut paper.
Dave