Well, I finally did as others on this forum suggested.
Even though I truly feel end users should not be expected to do it, I removed the battery, pushed the power button to discharge any remaining power, removed the heatsink from the processor and scraped it off with a plastic switch plate, cleaned it with 91% isopropyl alcohol, rubbed Arctic Silver 5 into the cleaned heatsink, wiped it clean with a coffee filter, and put a tiny (1/4 rice grain sized) dab of AS5 on the cpu, tightened the screws, and sweated bullets as my m6805 was started.
Guess what? No smoke or fire!! It started and is running without the cooling fan running. (Recently the cooling fan ran ALL THE TIME, even on 800 Mhz.) It is once again quiet. It is too early to say my auto shutdown problem has ended, since it happens with no predictable pattern or timing.
One observation: the old thermal pad had a little 1 inch x 1 inch piece of metal foil between the heatsink and processor. Is that usual?