Additional info: So today, Oct 11th, got ready to head on out and slides wouldn't work. Kinda expected that so set up an electric space heater with fan on a step stool around a foot from the hydraulic slide assembly. I'd been waiting since 9ish and tested several times just trying to pull in the slides before I went with the heater. Only ran it around 5 minutes and the slides started working. Air temp was 44F. Ok, after a night of 20F, close enough to the temp that previously made it work so could be a coincidence.
Pulled in the slides (once they start working, always work) and since it was 11 am by then, decide to spend the night here. Left the slides retracted. Just checked again hours later, with the air temp at 37F, and I can hear the pump runs when I press 'Retract' for a test (just to make sure it hasn't failed again at that temp).
Now, that suggests latent heat in that massive mostly metal assembly (see picture above) is helping keep it operating at that low temp. I'm certainly not going to extend the slides now for a test since I'm leaving tomorrow AM.
I did spend some time today inspecting connections down there and didn't really find anything wrong. Starting to think maybe Mr. Wizard might be right with his call of a bad solenoid. Has the signs pointing to something like that. Because of the temp dependent latency.
Two days from now, should be where it's fairly warm.
Kind of an interesting problem. Hope I'm not boring you all.