New cooker is already at work cooking 3 weeks worth of my lunch casserole(?).
Time to investigate my old balky slow cooker. It was harder to get apart than expected, but I was able to get it apart.
I didn't see any obvious fault revealing the known problems; (1) balky switching, (2) occasional difficulty booting up.
I tried to probe the tact switches to confirm switch action, and while difficult to probe both leads and push the switch with only two hands the tact switches are clearly not behaving well.... I only see two electrolytic caps on the processor board. 100 uF at 10V seems large for the typical power on reset circuit, I suspect that is what they are... It seems unlikely the cap is so leaky it fails to charge up enough to reset, but for a few cents I can replace them.
I have new tact switches on order, and some new caps,,, $3 worth of parts and $5 for cheapest shipping option.
I will need to scrape adhesive off the screws holding a relay board to the back of the processor board, but not today.
While no definitive smoking gun was found I notice that several bare wire jumpers and switch leads looked tarnished. My new theory to explain the failure is the thermal igloo I keep the slow cooker inside, traps humidity from the cooking food, that resulted in premature degradation of the tact switch contacts.
Now I need to think about how to prevent a similar trajectory for my new cooker. One obvious thought is to lose the thermal igloo, another is perhaps a more moisture tight lid seal.
Now I need to collect all the random screws for future reassembly.