well I said IF possible. It would just work better.
Dave Jones I think was making some threads about some great flux remover he found, and he had excellent results with just soaking it (non ultrasonic IIRC). Alot of people don't like ultrasonic because of concerns about damaging certain parts (i.e. crystal oscillator)
For making a hot board generally smell less, if its smelling after you are sure its clean, there is a few hacks you can do, that usually is to find components that are getting hot and attempt to isolate them from the PCB. But I think phenolic has a very characteristic smell, and its not similar to flux..
For instance,
-a resistor that is at board level can be lifted with some standoffs to prevent it from heating the board (it gets better airflow and its farther from board).
-sometimes it might be possible to add a small clip on heatsink to some transistors
https://www.diyaudio.com/community/attachments/metal-spacers-jpg.309482/I have seen all sorts of what I call bad design decisions around CRT stuff. They seem to kind of have a problem of running pretty hot.
I personally had to go through 2 big cans of flux remover to clean this one board last year, that shit would just not get clean. It does work, but not nearly as good as they claim IMO