Sorta deja vu.
I had posted this in another thread last week...
My MSD 6AL (PN 6420) died a couple of months ago. Started failing on hot restarts a couple of times then nada. Shock mounts under the dash were intact and external heat not an issue. Age was though as it was 13 yrs old. Using a 30x Loupe I found Tin Whiskers in 3 areas of the PCB.
http://nepp.nasa.gov/whisker/index.html