Thanks NGY!
I took the mechanism apart again and found that the left most micro switch was completely trashed. Using image search, it seems be a C&K HDP Series Micro Mini, Side-Actuated SMD Detect Switch.
Digikey: https://www.digikey.co.uk/en/product-highlight/c/ck-components/hdp-series-micro-mini-side-actuated-smd-detect-switches
Here is a rough video of the problem:
This is my week for fixing Sony Minidisk machines. I also have an MDS-E10 which is not well and awaiting a new belt. I'll be back!
Regards,
John O