There's a good chance I can repair your tach. Send me a PM.
It's a good idea to clean and lube them every now and then (every five or ten years?) to prevent major distruction. The speedo should probably be serviced if you don't know how long it's been since the last time, especially considering the fate of its neighbor.
Wanted: Dead, smashed, crashed or trashed gauges
BMW GAUGE REPAIRS - TACH*SPEEDO*CLOCK*VOLT METER *PODs & LIGHT BOARD*