Sorry to hear that Brendan, however it is a common fault with D3's at the 4year mark. I went on the D3 forum and followed the instructions with new parts to fix it myself. Dealer cost often quoted at ~£600 if they know what they are doing that is; cost me about ~£20 for a 'suppresor assembly' under the gearbox. A bit awkward to fix but doable. Then you will need to re-calibrate the selector positions as the assembly and the selector detector are held closely together. Yes you will also get lots of faults showing as a result.
Pic shown below of my rusted one and the new one.