Thanks warp
Well you have 3 options to replace it really
1. Find a (superseded) 10-13 Roadster GPS unit (3 pin plug) somewhere so you can just replace the GPS itself and wait for it to go bad again
2. Replace the GPS (4 pin plug) along with the 'fly lead' adapter harness, and do the small wiring job on the tacho, and it's fixed forever
3. Replace the entire wiring loom (includes GPS) and clocks with 2013+ ones, and map the ECU with a 2013+ Roadster map, and it's fixed forever
The wire thing in the tacho is really simple to be fair.