Hi Chris and welcome to THE JAGUAR OWNERS CLUB. Have not experienced any issues with the speedo sorry therefore, cannot assist you there. I'm sure there will be someone seeing your post that may have a better understanding however, failing that I would suggest you contact an Independent Jaguar specialist, it cannot be that much of a problem seeing you already have a replacement.
Let us know how you get on so that we can arm ourselves with the knowledge should another face the same problem