I posted this in south Australia section.
If you are having problems with the key just check the circuit board. It's quite easy to remove and put back
Mine had all this contamination. Easily cleaned with IPA

 

Looks like the rubber cover came loose and moisture got in. Never good for PCBs

 

Those Jaguar rubber covers are uesless. I bought a couple of these https://www.aliexpress.com/item/1005...37731802T7XjQm
work very well.

 

Are those add on covers or replacement for the bonded rubber? The bonded rubber it the problem I see. I have a key (was the PO primary key) that the rubber has become unglued from the key body and I can see directly onto the PCB. This would appear to be the cause of the the OP's problem.

 

Thiose add on covers go over the entire fob including the rubber. These are rubbish but the covers are excellent.

 

The video in the advert shows how to assemble it. You do need to take off the little split ring. See pic.