In order to properly repair a plaster problem, you need to know, if possible, what caused it.
In your case, you mentioned your house was 45 yrs. old. It is likely that the plaster system used in your house is plaster base and topcoat over gypsum lathe.
Basically you probobly have a drywall-like product acting as lathe (or backing) instead of strips of wood, which were used in earlier houses.
If that is the case, it would explain why the crack reappeared so quickly.
The problem is one of too much weight(from the plaster) pulling on your gypsum lathe and the system (usually metal clips) used to fasten it to the joists. In other words, a structual problem.
I encounter this frequently in the Peidmont of North Carolina among houses of your time period.
There is a solution and it basically involves securing your ceiling back to the joists before repairing the crack.
I am planning to produce a number of videos on plaster repairs in general and this particular repair problem and others in the near future, but if you would like specific instructions on how to repair this problem, I would be glad to walk you through it.
Contact me, Philip, at Estate Plaster, Inc.
1-336-691-1767 between 6:00 pm and 9:00 pm EST, Mon. - Friday.