Hi Larry,
It's not your problem as you describe, but I was told from a Equipment Hire place that one big problem with these impedance analysers (and similar age LCR meters) is that some stuff in the front end drifts/goes out of whack and the unit can no longer get into range to make a measurement.
My thought is that apart from the obvious electrolytic capacitors it might be worth checking any silver mica types that only have low voltages across them (e.g. bjt voltage drop) as they can grow whiskers (ironically it seems to be low voltage use of high(ish) voltage rated parts that is the problem).
Anyway, just a random musing.
Best,
Susan.
Susan Parker