Door handle is finally working again.
I took the Z4 over to my Lexus specialist. A lot of muttering under his breath but he will occasionally slum it on German cars
First thing we found was that after the door card had been removed every clip was either broken off or squashed. That'll explain the rattles then. Someone had indeed been there before as the membrane was torn and after much swearing the Bowden cable was swapped. The old one had definitely seen better days. But once fitted the door handle still didn't open the door. So then they tried swapping the the original handle for the spare that came with the car. Looked identical but you never know. That didn't work either.
Attention then turned to the latch mechanism itself. Once it was out it was clear that it was a non-genuine part. As it happened there was another in the same box of bits as the handle. This time genuine but used. Fitted that and everything worked perfectly. Re-fitted the original handle, replaced all the clips and the door card went back on, the door now closing with a much more satisfying clunk.
So little mysteries. Why had someone been in there, not replaced the cable, fitted a Chinesium door latch, bought another handle (originally red and sprayed silver) and also bought another door latch? Or had they tried to fix the issue by changing the latch but it was in fact the cable, the new latch made things worse and the original is what was re-fitted today? We'll never know.
And while it was there we got it up on the lift, fitted the Osram Night Breakers (another parts box find) and then gave the roof drains a good blast with the air line.
A good day. Even got to drop the roof on the way back.