A common failure mode for gas plasma dot matrix displays is for a lead to
break right where it enters the glass. The lack of lead sticking out means
nothing for solder to connect firmly to. A solder job, if successful, will
work for a short time only.
A great repair for this is using conductive epoxy. Lift the lead, put a dab
under the lead, where it enters the glass sandwich, and push the lead back
down. Use enough to allow for the lead springing up, but not so much you
get a short to the adjacent column or row.
This fix will last, and is moderately durable. It has survived a local
truck ride, but failed during a 400 mile trip. It can be repaired again if
the epoxy lifts off the glass.
The conductive epoxy is available at some electronic supply houses, comes in
a pair of small tubes, and costs about $15.