I remember my Austin Maxi having a similar setup, with the jack arm sliding into a tube.
While changing a flat the whole car began to drop slowly and to one side with an ominous creaking sound!
The reason.....good old British Leyland rust!
The warning signs were there, flappy door bottoms and a hand size hole in the tailgate. It was 8 yrs old at the time so what would you expect
Luckily I used the wheel under the car trick, so was able to get the wheel back on somehow, and I still tend to do this now.
A great car though for the time, not unlike our A2’s transverse engine, 5 speed, hatchback, etc. It even looked quite modern when introduced, however crap cable gear change and the above mentioned rust being the main problems I recall.
Still remember the reg on it FKT 573L my 2nd ever car.