Thanks for the reply. I'll away out to the box of small metric machine screws in the workshop and see if I can find a couple of matches. ll need to turn them down to ball-ish ends in the Dremel to make sure they depress the O rings just enough to prevent the sheering as they pass over the grub screw...

Any recommendations on how to slide the barrel back into its housing without nipping the edges off the two O rings (listed as #58) as the barrel passes over the openings for the two retaining grub screws? On taking out the grub screws I found there were little slivers of rubber underneath each of th...