Look what I found.
Strange properties. It appears to soften a little with water - turns transparent yellow rubbery - but not like hide glue. it becomes white milky strings if placed in water. In places it is extremely hard and does not soften at all. It does not smell like hide glue.
Actually, I think its a combination of hide glue, PVA and urea formaldehyde or araldite, all dribbled into the cavity about 40 years ago. Yuk.
Virtually NO actual contact between neck and block at all!
I guess this is common, yeah?