Thanks for those "tips" about the caps. Yes, they look "beyond awful" but yes, it is mostly external. The speckled yellowish axial caps are Sprague "TE" types, they have a soft poly sleeving which seems to have reacted with the storage conditions (garage) over a decade or so. It can easily be scraped away and is a waxy sort of substance. The circuit boards are all conformal coated and these caps may have been coated with something as well, not sure. At any rate, I have actually checked each and every one (in circuit) using a handy capacitance/esr meter. I found only one that definitely needed replacement - it was a small (10 uf at 25v) one that had gone open.
I have reposted this topic in the Repairs section, I agree that it probably belongs there, although the unit is a piece of calibration equipment. Thank you all for your comments. I really hope to luck out and find someone who has a schematic or even better a manual for this.
In closing, at this point I have a working calibrator, but the output is not stable. I have traced out a lot of the signal flow from card to card, but don't really understand how the output level is regulated (I have found a "black box" on one card which is completely unlabeled but I suspect is a thermo-electric ac-dc converter for the control loop) but I really need some sort of "how is it supposed to work, as designed" resource!