Very pleased to report that the KD21 (KD21AC on the door panel) Superba Whisper Quite is working near perfectly and that I couldn't be more pleased.
When we fired it up I noticed that buttons were sticky and that the cycle timer was notably loud. I thought this must be related to the air dry feature, where it must blow the air out through the door panel rather than a fixed vent.
I noted that there was a dusty white powder on the drain cog which must have once been grease and would confirm the movement of hot air in the clock and switch gear.
So - I removed the control panel and applied a very light dab of 'Honey Goo' (NAPA) lube to the button blades, the primary timer gear wheel and the drain cog.
WD40 and similiar anti-seize lube simply washes out the contact surface and about a week later - leaves the clock parts running on bare surfaces and often now gritty plastic-to-metal surfaces.
We dealt with something like this on our vintage motorhome, so I can assure folks that while they built these to really last - what lubrication as is left has likely long ago failed and will prove to be a very costly repair if not dealt with upon re-light.
The 'Honey Goo' product is a food safe penetrating lube that usually doesn't require a re-application for several months. It will clean out the matting surfaces of any debris or dry grease as it runs.
The trick here is not to use too much Goo - but just enough to make sure that the parts aren't rubbing dry on one another.
This was easily achived by tripping 'normal wash' - then hitting cancel and popping a little dab of spray at 1/4 turns on the gear and cog. Takes about 60 seconds for it to cycle completely - I did it twice, then wiped off any excess I could get at with a paper towel.
Later - I'll re-apply the white-lithum grease that must have came from the Singer Control factory and leave it alone for the next 25 years.
Next up - the microfilter for the pump-top. I'm sure I now know what it is made of and will try to make up a replacement mat.