What would a German mechanic say? Ihre Übertragung ist kaput.

Either an o-ring(s) has/have split or the A-drum has shattered. My guess will be that the A-drum had shattered and the shredding sound that you heard was the clutch plates grinding against one another because they are no longer retain by the A-drum.

You can Google ZF 5HP24 A-drum bad and o-rings split.

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2006 Infiniti G35
2001 BMW 3.0I E53 X5 Build date 08/2000 SOLD
Lotus Europa 1970 Destroyed by fire
Lotus Europa 1970 S2 Renault Powered
Lotus Type 52 1970 Twincam Webers Powered
PORSCHE 911 Targa 1982 The Garage Queen
Audi Avant donated to Kars for Kids
BMW 525IT Sold
Audi 4000CS Quattro Sold
Jensen Healey Lotus Powered Sold
Opel 1900 Sold
Triumph Spitfire 1971 Sold
Triumph Spitfire 1968 Sold
Plymouth "Cuda" 340 Six pack SOLD