weeeell, time to rip it apart! unfortunately it does require pullin the gauge assembly out the front, which means disconnecting the wiring - can be done from underneath, but the screws that hold the speedo into the cluster are tiny and ya hafta work half blind - I did it after the 4th or 5th time I hadta pull the thing apart!
I can take some pics of one I've already got out if ya think it'd help
Bill