Not that is adds to the discussion, but by my count there have been 7 Nimbus 4D’s that have suffered spin/spiral wings break off.
The owner of a local N4D replace a metal bracket thingy in the elevator assembly on his 18 year old glider, it was the same part number for a
Dou discus and Arcus. Lots of common parts in the tail feathers of all twin place S-H gliders. Sure would be nice to know failure mode.