I used DOT 5 brake fluid (not DOT 5.1 which is NOT silicone). It seems to work fine. My appliance has a slight hum, which might indicate damage to the heating element from being operated dry. So far, no other issues.
I doubt if another 12,000 would have made much of a difference to me. My brother was living in Bloomington at the time, working as an engineer at Westinghouse. His guidance during those years would have been helpful. Although, now that I think about it, if wishes were horses, I should have gone...
There were 17,000 enrolled at Bloomington in 1968. My high school class was 84 students. It felt too big for me, I went to Evansville. In retrospect, I should have gone to Bloomington.
And ... 13 years later ... someone has the same issue!
I found the fill port. See my essay at https://johndyerwrites.com/2023/03/22/unfulfilled/
The oil chamber is filled with high temperature silicone heat transfer fluid. I'm going to try DOT 5 brake fluid. I'll post results.