...on my '93 Si.

The dash has never been messed with, apart from me removing the driver side tweeter cover to custom mount my AEM gauge-type UEGO controller. The odometer and tripmeter have not worked at all for me since buying the car...but everything else seems to work fine.

Is there some sort of a fix for this, or do I need a new gauge cluster?

 

if your tach is working and everything else works I'm sure the VSS (speed sensor) needs to be replaced

 

If the speed sensor was faulty, wouldn't the speedometer not work?