had it months and months..or longer, get out your cupronil or any
liquid- battern's flux for example, squirt out the paste, mix it
to the right consistency and draw it up into the syringe and cap
tight- or leave in a bit of water or glycerine to cover the
needle's tip if using it daily for production, etc....
Another good liquid for mixing with paste solder that’s become stiff
& dried out is mineral spirits. Add 3 or 4 drops, mix & test before
adding any more. It doesn’t take much.
If you keep a syringe or 2 on your bench & don’t remove the needles,
a good way to to plug the needles is with a piece of music wire. Take
each size needle you use with you to the hardware store & select a
piece of music wire that just fits into the needle.
When you get home cut off about a 2 inch (80 mm) piece of the wire &
put a 90 degree bend in it about 1/4 inch (6mm) from one end. This
will act as a handle & make it a little easier to pick up off a flat
surface.When picking it up from a flat surface, rub your finger
across the wire. This will cause it to roll & you’ll be able to
grasp the wire.
I’ve used this method for years.