96 D1 SD.
So, if I'm inside and pushing down the driver side lever, it'll lock and open all doors.
If I'm outside, and push down the lever, it'l lock then come back up a second later.
The key rotates in the cylinder loosely in all directions.
I'd bought the plastic bits to a body shop here but they gave up on the job.
Also mentioned a wire attached to the mechanism had been cut.
ANy thoughts on what I need to replace? many thanks, and safe holidays all.

 

Wires cut at the lock mechanism sounds like they cut the lever switch.

If the key is rotating and not triggering anything - there is a plastic cam in there that can break.

A photo of your door lock assembly might be helpful.