Pedro has it right, except that my info is the mileage from the old instrument cluster can be moved to the repaired or replacement cluster.
At least this is what I was told when I was faced with possibly replacing part of my Boxster's instrument cluster because of an always on airbag warning light. The tech (at the VDO repair facility in AZ) talked to me over the phone and described various ways of fixing a bad instrument cluster. Parts can be unsoldered and new parts soldered down. The contents of the FLASH memory chip can be read and then written to a new/replacement chip. There are a number of ways and he didn't seem concerned that he would not be able to preserve my car's odometer reading even if he had to replace the original one with one salvaged from another car and "rebuilt".
My advice is to find a highly regarded automobile speedo (instrument cluster) repair shop in your area and speak with someone there to find out what can be done.
I was recommended to use VDO Repair (www.vdorepair.com) and did use it. Well, the Porsche tech removed the instrument cluster and the parts manager packaged it and shipped it to the repair facility in AZ. However, I can't seem to locate the link for VDO Repair. Perhaps it has gone out of business?
Here in northern CA, there is Palo Alto Speedometer (in Palo Alto CA) which comes in for very good word of mouth praise for its instrument cluster repair. Here is its link:
[
paspeedo.com]
While you may not be in the area, but more distant, it doesn't matter so much where the shop is located as the cluster is small enough, light enough shipping is not that expensive. You need to speak to the shop before you ship though to be sure it can help you, confirm that the odometer reading can be preserved, and what the repair will cost and how to ship and what insurance if any should be on the cluster.