On Wed, 22 Dec 2004 05:15:23 -0800, Roy Lewallen wrote:

(snip)

Before introducing a new instrument, we went through a lengthy process
of building and testing prototypes, which I described some time ago in
this newsgroup. In one group, it was our practice to borrow some
assemblers from production to build the prototypes. One afternoon I was
looking at some units they had built, after they had left for the day,
and saw that the plastic of some switch bodies was very badly crazed --
they were covered with tiny cracks. Some experiments with bottles of
solvent we found in some of the assemblers' work areas pinned it down to
one particular liquid. The problem was one of the ingredients, which was
a relatively common solvent of the time. Unfortunately, I don't recall
which one -- it was something pretty mild as solvents go, like toluene
or Freon, not a relatively strong solvent like acetone, which we all
knew better than to use. We found out that the solvent had been banned
from production, but the assemblers kept a supply out of sight because
it was really good at removing flux.

May well have been toluene. It was often used as a cleaner in all sorts of
areas, some as pedestrian as the T/R/S plugs on old lamp-signalling telephone
switchboards. Unfortunately proved to be a carcinogen and was banned, but it
WAS used to clean a myriad of hardware in a myriad of situations.