It's interesting to hear these stories from those who were there at the time, and heartening to see that with good management us Brits could still turn out a solid product
Now you mention it, the PCB probably did have some electrical leakage going on too on my old set, a kerbside rescue used as my main set for 8 years or so, (as well as the cold linearity issue) it used to make an occasional crack/snap like something had arced, even after repairing the cracked PCB and frame IC joints and cleaning all the dirt out (I like a clean chassis even if it doesn't make much difference to how it works, it's just "nicer" that way). Never made a difference if it was humid or dry & never affected the picture, just occasionally went crack! After I failed to find a probable cause, just decided to let the set run and see if it developed, never did...