Data Point One:

I have a Sony stereo receiver purchased in Japan in 1970.  When I opened 
it for some repair work, I saw that the main circuit board was 
completely covered with flux.  Not a little here or there; entirely 
coated.  Every other audio/video/TV product from that era I ever opened 
up was also covered in flux.

Yet over 35 years later, they still work as well as new.


Data Point Two:

Taking so-called "NASA qualified" soldering classes in college, removal 
of all flux was absolutely mandatory.  And flux is well known to 
complicate life if the board was dirty or contaminated before the flux 
was applied.  It never hurts to have it removed.  Yet, I always wonder 
about Data Point One.
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