Check out http://www.odometergears.com/. I used the gears available from this guy to fix my SDL speedometer. Prices seem a bit high, but then again, if you take the unit to a speedoshop, I don't think you will get out of there for less than $100.

__________________
as ever
Paul

1989 560SL
1987 300SDL
1987 300TD
1983 BMW 633CSi
1972 280SE 4.5