[Milsurplus] BC-348 Ant RF unit - freaky capacitor mystery

[john p hutchins]

Group -
Question on this mystery, actually 2 mysteries:

While attempting to align the BC-348;  Noticed that the Antenna RF unit 
would not "adjust", enhance or detract,  signal strength from the signal 
generator.  I have pulled the unit and inspected its contents this is 
what I have found:

Antenna trimmer blown edge off rear plate with a dangling melted metal 
stalagmite!  That accounted for the static on one half of the rotation 
of the Antenna trimmer!

Further examination found, Band 4, trimmer capacitor with significant 
outside plate damage, about 1/4 melted away.  The silver mica 300WVDC 
connected across this trimmer capacitor when checked with my Sencore Z 
meter showed capacitance within tolerance and capacitor passed Voltage 
leakage test;  Mystery Why /How was this capacitor not fried?

Further checking of the capacitors I found .01uF 500WVDC mica on band 2 
Tuning Padder capacitor value measured 8350pF  After passing 300WVDC 
leakage testing, re-measured the capacitor its value was 9500pF.  After 
an hour I re-measured the capacitor, the value had fallen to 8350pF.  I 
am replacing the capacitor. Why the value drift if the leakage test passed?

Thank you
John Hutchins