RE: Glue - How old is safe?
I wouldn't take a chance. Use some thin CA and just put a bit on each joint. It soaks in and creates a good bond, although I'm not sure it will stick to the existing glue.
This has almost nothing to do you with your question, but I have 25 year Sig Ment that I used to build my trainer 25 years ago, and its still as strong as the day I built it.
Jason