Mod 358, ser 5-13. I'd not noticed before but there is a lot of axial movement of the chuck. Normal or worn ? Went inside , needed a clean out and lubricating if nothing else. There is a wavy thin compression spring/washer on the axle but it is about 1mm away from the bearing, so about 2mm of possible movement between static and active use.
-- Diverse Devices, Southampton, England electronic hints and repair briefs , schematics/manuals list on