In article ,
Ross Herbert wrote:

snip
I would resort to a pure liquid activated flux which sadly is no longer
produced, Magna Alloys type 87. I still have a small quantity left but when
that
is gone...

We use Kester 1544 for hand soldering, and desoldering as well. It's
fully activated and works very well. At 50% solids content, it's too
thick for a foaming flux bath, but works well in a capillary dispenser
for hand work. Maybe you have a Kester distributor there? They produce a
large and varied flux line.