Dave,

Same thing happened to mine.  I didn't want to risk messing up the odometer trying to fix it myself.  I took the speedometer to a guy here in Austin by the name of Rick Borth.  He does great work.  I think it cost me about $70 to have him fix the odometer/trip meter and clean/re-lube and calibrate the speedometer.
Check out his website at http://www.speedometer.com
Best of luck.

Jim Bowen
'88 Wolfsburg Weekender (Lola)
'74 Super Beetle Sun Bug (Goldie)