I wrote:

snip
OK, there's the problem, a dead mag.

I just received a call from my trusted mechanic early this morning.
He discovered that a capacitor failed in-flight, which in turn grounded
the mag.

This is a bit beyond my limited knowledge of aircraft mechanics and I
cannot correctly explain what a capacitor does, but the good news is
that it is much cheaper to replace a capacitor than a mag.

--
Peter