Recently, I restored a 1939 British glider.
It was casein.
There was not one glue failure in the entire project.
Not one.
It had been maintained in a proper manner. Varnish and such.
I have found that if the Casein is bad , the wood is bad too. If it has had
such poor care, the entire project should be in a museum and not flown.
Regards,
Bob Gaines
Marietta, GA