Honestly, I don't think you've got much of a choice. Either get your current one repaired or replace with a used similar unit.
I don't have any direct hands on, but I've read that neither the earlier NG900 nor the simpler 4 button OG9-3 SID's are plug and play.
I suspect if you had both a 4 button SID and it's wiring pig tail, you should be able to use the wiring color codes on the pig tail to work out what wires had to go where on the current SID's pig tail and modify the car's harness to properly use the 4 button SID.
There are a lot of DIY ideas on the 'net on how to repair the SID display. might be worth a try to try a DIY repair and if that fails, send the unit off.