Thanks Doug,

This is copper wiring. I do notice on the buss bar that there are two
sizes of screw terminals. The ones containing two wires are of the
larger size. However, the point is taken. When I do my "housekeeping"
on the panel, I will try to keep it one wire per terminal. It does
look like, however, that there may not be enough terminals for each
circuit to be in it's own, but I'll get a closer look. The last time I
worked closely with the panel is when I installed a 50A breaker and
wired in a sub-panel for my finished basement.

It definitely seems like a poor connection on the buss since it worked
fine for a week after tightening it. However, this morning it was back
to flickering and arching.

Thanks for your help.